If I'm understanding you, it's not the clip's timebase that you want to change to absolute time, but just the snap grid resolution. For that, you just right-click the snap interval, choose samples or seconds, and enter a suitable value.
Or if you're trying to align clips to transients in the drum track, enable the [Land]Marks button, set it to Audio Transients, enable Audiosnap on the drum track, and add its transients to the pool.