Did some really scrubby damage testing versus Stage 4 boss' first spellcard, which I can dodge with fairly minimal interference from bullets. The timer is 30 seconds, time listed is what's on the clock at clear time. This is with Summer in positions where no summer bullets hit the boss.
Reimu: 13.2 seconds (aka, she took about 17 seconds to clear the card)
Aya: 12.5 seconds (17.5 clear)
Marisa: 15 seconds (15 clear)
Cirno varies due to spread shot.
9 seconds, 21 clear (max distance)
12 seconds, 18 clear (mid distance that you're most likely to be at in general situations)
14.5 seconds, 15.5 clear (a couple character lengths away)
16 seconds, 14 clear (shotgun tier, some summer bullets hitting admittedly)
For non-Cirno shots, winter lets you clear about 2 seconds faster, Spring is 1.5 seconds faster, and autumn is inbetween those two if you move to the side a bit for Aya or Reimu (marisa would lose laser hits to do this). Keep in mind spell practice mode is lv3 season, not max. Still, it seems that the damage difference isn't significant between seasons unless you're at max level- granted, they have much different areas of hitting, and summer is... yeah.
I speculate that Reimu with ONLY her homing shots would take about 35 seconds to clear the card, meaning that pretty close (or exactly?) half of her damage is homing. Spring deals a negligible amount of homing damage by itself, and only brings speculated clear time down to like 32- of course, this is only lv3 spring, though.
