There is no set recording length. Resolume records until the computer runs out of memory, as this paragraph from the manual's chapter on recording explains:
Note that the record function is not intended as a full fledged video production tool. Instead it is meant to quickly record and then play back a content that has a few effects or modulations applied, so that for instance you do not have to continuously keep moving a fader to achieve a certain look.
If recording suddenly stops, this is because you have run out of memory. When recording, Resolume tries to write the rendered frame immediately. This is done at a very low priority, because you don't want this to interfere with the actual output. So when it's too busy (lots of effects/clips/pixels), it stores the rendered frame in memory, and tries to write it later. At a certain point, when the memory is 90% full, it will stop recording and write the remaining frames in memory.
If you want to record longer segments, you will either have to write to a faster drive, get more memory or lower your resolution.