Hi...
It's important to remember that the Timeline length and Project length can be two different things. The Timeline for example can be one length while the Project length can be less than the Timeline length (but not more).
The length of the Timeline is set in Project Settings (CTRL+SHIFT+P). This can be anything up to 54,000 frames or 15 minutes (@60fps).
The Project export range is set by the In/Out Markers (see number 14 below).
However, in the case of your particular render question, if you output 1218 frames to video with a frame rate of 30fps then you should get 609 frames (not sure about 604). But if you render @ 60fps you would get the full 1218 frames. Either way will not affect the actual length of the exported video. For example, a one minute export will still be one minute at 30fps or 60fps.

Peter
Forum Administrator
www.reallusion.com