I was in the same position last season, doing my first TTs. Got the bars 3 weeks before first race – yikes! Riding aerobars is a completely different world than riding aero on regular drop bars. You WILL need to practice, not just for power output but first and foremost for bike handling skills, esp if there’s wind!
Clip-ons are well worth the money and hassle. Be sure to get them set up properly (another reason to get them early!). Search the used for sale sites, there’s always some available for cheap and in great condition. Good luck!