If you’re using an M.2 SSD, now is as good a time as any to install it, because later on other parts may get in the way.
If you’re using an M.2 SSD, now is as good a time as any to install it, because later on other parts may get in the way. You could also do this step earlier in the process, as an M.2 drive is small and lives flat against the board, so it won't get in the way of anything else.