I strongly recommend using a decent NLE. I use Vegas. It has a great advantage for videos like yours, for two reasons: it lets you directly import image sequences (i.e., a series of stills); and it was originally an audio editor, so it lets you do all sorts of things with audio.
I am always amazed by how often people use AVISynth for things that could be done so much more easily, and with much greater artistic freedom, if they would just use an NLE.
[edit] BTW, I too do a lot of time lapse. They are trivial to do in Vegas:
Carmel Valley Road at 250 mph
Time-lapse of the Carmel Soberanes Fire in Garrapata State Park