In this situation, all you can do is serve the tenant with the N4 whenever he does not pay on the due date. However, if he does pay the rent after receiving the N4, then the notice is void and you would have to wait until the next time it happens and serve him again. You have mentioned that he has a lease until May so all you can do until then is keep serving the N4 when he’s late. The N8 notice for persistent late payments cannot be served until 60 days prior to the expiry of the lease, so the N8 you give him now would be considered invalid.