You can do your return as late as 31 October but the sooner you do it, the sooner you can use the money refunded to you (if you some). Especially if you want compounding effects.
I email my tracker to my agent on 1st July, they usually have claim submitted within a week, my refund is often done within another 2 weeks. The refund goes straight into my WISE account by end of July and then it’s time to decide what to do with it.
You could: