You can add CYA at any time. But you probably don't need it right now until the new season starts ramping up.
Also, anytime you raise CYA substantially (more than 10),
Overnight Chlorine Loss Test first, like now, with going from 40 to 70. The SLAM slam target will increase from 16 to 28, and you'd hate to find out that you need to slam in a couple weeks. So prove that the water is algae free before you ever spike the CYA.
But again, for the next month or two is probably fine at 40. You'll know when the daily loss increases considerably that its time.
Grab some and add a couple drops of muriatic acid to it. (Somewhere that the acid won't ruin the work area). If it fizzes its calcium and the fix will be to lower the TA.