Martin,

there are two possible approaches to add timelapse sequences.

1st way:it is available setting a new default  frame duration before to drag/move the frames to Timeline. In my opinion, this way is not the optimal. because it requires too much mouse clicks. To change default frame duration go to Menu FILE > Preferences (F5) > Timeline configuration : Default Still/Title Duration (it is near the right bottom corner). Now moving frames to Timeline they should have 1 Frame duration. also you could have to change the aspect from unknown to 1:1/4:3/16:9

2nd way: it is available from Repository window, mouse button right click  ADD IMAGE SEQUENCES so now you can point the first Image file and specify frame rate , target video mode (576i/1080i/1080p etc.) , aspect and duration. If the frames have the right file names (BASENAME_XXXXXX) you will get a clip with all your desired frames. I can suggest to use Renamer free app to rename all frames to match the right name scheme. Moreover to play them in realtime without drop frames you could have to scale down them before to collect them.All depends from your pc power, disk speed and Image size.

enjoy!

Roberto Castellano