@shreedhar I think I was unclear. what I meant is to start RT from the command line, but passing it a raw file as argument. something like this:
rawtherapee-test.exe "c:\my pictures\awesome.nef"
this activates a āsimplifiedā mode without the file browser. could you please try this and report the time? thanks again!
I did what you said and the time was down to about 17 seconds from the 25 seconds. I put the image file in the C: drive itself, no folders. Also, RT did open just the editor tab, without the file browser.
thanks, this is helpful. Iāll dig deeper
As silly as it sounds, on Win 10 one can try running a program with no internet connection. If āSmartScreenā feature is doing things in the background (checking everything unknown against MS databases), it will warn you, that it needs connection. At least for such issues, I would disable it completely. (The option to do this is getting more hidden with time.)
Any downloaded installerās settings can reveal, that it is āfrom unknown sourceā and so āblockedā. āUnblockingā it manually prevents one additional warning.
AV programs, at least some, also can change their own settings silently when āupgradedā. I certainly didnāt alert anybody yesterday to get this message:
All this might not be relevant here, but trying to control all the Windows security software as much as possible can be sensible when developers are dealing with funny behaviour that only happens on some systems.
Iāve tested the custom-file-chooser-button branch and didnāt find any issue. The startup time on my old dual core i3 2.9 GHz was 12 sec. and now it takes only 5 sec. 
So far, so good.
Even hours later, and several resume-from-sleep cycles, RT is still launching in less then 2 seconds! Even on dirs with dozens of large image files!
More remarkable: when I launch the original rawtherapee.exe it again takes about 50 seconds to start! 
and clicking on the āpreferencesā button, takes at least another 20 seconds to appear.
But when I try the rawtherapee-test.exe; everything is quick & responsive immediately! Not even a restart is necessary. So there were definitely compile (?) bugs/errors in the original RT 5.3 for Windows release.
No, @agriggio just greatly worked around this bugs in gtk3. It may happen that you experience the 20/50 seconds delay now and then when you press one of the file chooser buttons 
Ok, but I tried to say that the 5.3 Windows release contains the non-fixed, not-worked-around bugs in gtk3. And that the -test.exe Iāve tried today launched and responded almost instantly.
I understand that the complete workaround is not yet done? And we (= users of RT) still have to do more testing/digging/using the product?
Yes, itās correct that rt 5.3 (and also pre 5.3 gtk3 builds of rt) on Windows suffer from this slowness on some systems. Currently @agriggio made a great workaround to this special behaviour of the file chooser buttons which I really appreciate
I do admit that Iām having quite some difficulty following this thread - I donāt have a clue about programmingā¦
Maybe Iām simply too patient? I never worried about the time RT needed to start; I simply waited until it was up and running - and then it worked without any kind of problems. After reading (and trying to understand) this thread I tried deactivating the formats that I donāt use or (most probably) wonāt be needing. As a result my RT 5.3 now starts in app. 7 sec. instead of app. 12 sec. beforeā¦
More than good enough for me! 
Just wonderingā¦
It was clear that the āspecialā rawtherapee-test.exe version was much, much faster. And it seem to be working ok.
Thanks to @agriggio (?). But why is this version still not released and/or available @ the regular download section of the RT website?
http://rawtherapee.com/downloads
A new release will be made soon, possibly in the next week.
Iām eagerly waiting for the new releaseā¦
FYI:
Iāve updated my system to Fall Creators Update 1709 Win 10.0.16299 and the startup time of the rawtherapee-test.exe version is now 3 seconds in a directory with dozens of large images! The āPreferencesā Window appears almost instantly, when I click that icon.
And when started for the second time, (from cache), rawtherapee-test.exe starts in under 2 seconds when started with an empty directory (no images)
We were going to release 5.3.1 with mostly speedups and fixes but without new features, but much has happened in the last few weeks, so it looks like weāll make the usual large new release when things stabilize.
RawTherapee 5.4 Roadmap:
@Morgan_Hardwood I canāt wait. 
Maybe something else to consider regarding startup time:
Most programs start within a few seconds, but display their first window/screen/messages almost instantly and after that, the rest of the initialization continues.
E.g. with PS CC 2018; you see the logo screen appear immediately after starting the program, then you will notice some messages scrolling through the logo screen and finally the program is ready for use.
The same with for example, Microsoft Office programs.
Seems to be something psychological? First display any kind of picture/logo/message, so that the user has a confirmation that there is something happening, and in the background, the rest of the entire software package is loaded & initialized.
Tip for RawTherapee also?
E.g. start RT, display a kind of startup logo and/or window frame, let some single messages scroll through a window, as to let the user know the program is doing something, and then finally open up the final RT full screen window?
Or something like thatā¦
Very good point about the āinitial displayā thing, it certainly improve peopleās impression towards a software regarding startup speed.
Unfortunately this is not my case. While RT 4.x started quickly here (i7-5960x, 32G, Win 10 Creator and SSD), it took almost 5 minutes to start 5.2. For 5.3, when I click and try to start the program, it appear in the task manager for one or two minutes (but nothing else), and disappears afterwards as if Iāve never clicked anything before. So Iām sure the issue isnāt entirely psychological.
@Peter_LO Did you try the rawtherapee-test.exe? Which was made available by @agriggio ?
Just read back some posts in this thread.
Thank you for the advice, PanoMeister. But the only difference is that the -test version disappears from Task Manager a bit sooner, as shown in the video clip:
Iām having problems updating to RawTherapee 5.3 on Kubuntu.
I followed the instructions on the RT site:
Open the terminal and paste this code into it:
sudo add-apt-repository ppa:dhor/myway
sudo apt-get update
sudo apt-get install rawtherapee
But then I get:
rawtherapee is already the newest version (5.1-1dhor~yakkety).
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
When I open RT itās still 5.1.
Any suggestions? Thanks.