I don't wait until the hunting season is almost upon me to try out my broadheads.
I periodically check them throughout the year. At least once a month.

If you're going to hunt, you've got to practice with broadheads --period.
Broadheads can amplify any error in tuning, and will often impact a different point than your field tips if everything's not quite right.

To make sure you don't have a problem, shoot field tips and broadheads at a variety of ranges.
For example, if you only shoot at the standard 20 yards all the time, and your broadheads are hitting th esame spot as you field tips, GREAT! ...but if you shoot at 30 or 10, you may find out that the arrow is oscillating more and not hitting corectly. The problem may not be evident at all ranges, since the arrow will be in mid oscillation and can appear to be bahaving properly.

Here's another tip I use.
To help visualize a good hit on an animal while shooting the sometimes fussy broadheads, I keep a cardboard 2-d deer target handy for shooting at last thing before going to bed the night before a hunt. I throw on some of my hunting gear, load up a broadhead, and send that razor right through the center of his lungs. I don't shoot at it all the time, but doing so with a broadhead, with my gear on, and while focusing on my sights instead of the deer helps build confidence in myself and my equipment, and reduces buck fever.