The only problem with being told this is Garth'zel didn't give Anakin a time frame, so he doesn't know how long he actually has to do anything.

Which means practice first, not that he minds it, and anything else if he has time. Which it turns out he does, even if he's not sure what to do. So he just takes time to wander and get to know the ship better, trusting Garth'zel will be able to let him know when he's supposed to show up.