Loop time is only 60-sec mono and 30-sec stereo. Not the best length in the world, I admit. However, HELIX is an effects processor and amp modeling appliance first and foremost; that does a damn good job, if you ask me. It ain't gonna do the dishes for ya though. If the looper isn't as long as say, maybe a BOSS RC-3, and you need a longer loop time. Just get an RC-3 or something like that.
The cool thing is, if you had a HELIX, you can take that Boss RC-3 and put in one of four effects loops, and just add it as a block in your chain. That'll give you the best of both.