Also note that your videos will always be decoded and re-encoded when using Natron.
A video editor may have better strategies and avoid re-encoding parts of the video (just like you would cut an actual photographic film).
I would add Shotcut and Kdenlive to Omar’s list.
The TimeOffset node may be useful too.
Also note that Natron’s Dope Sheet allows to move these effects in time (kind of) easily.