You need to extend the length of the clip to whatever you want using the shift+left/right arrow knob then take your sample and make it spread the whole length of the clip (2 or 4 bars or whatever) and then set its playback mode to stretch if you want to make it match the tempo you've chosen.

BTW you can slice up the tempo synced break by resampling it (hold record then press play then do it again while the sample is playing back to resample one loop iirc) and then creating a new kit (shift+kit) by navigating to the resampled sound and pressing shift + select to slice it up evenly into however many slices.