Question about tuition deadline on the 31st.

I work and get paid on the 17th, and the 31st. I could pay my tuition on the 17th but I’d be broke as hell for the next 2 weeks. Since my pay day on the 31st falls on the same day as the tuition deadline, would I be okay to pay on the 31st? Or would it not load/register the payment in time? Does it reflect instantly?