Thank you for reaching out to us.
We appreciate your dedication to immersing on time. Though an immersion at the beach can be valid, one of the halachic criteria for this is safety. We cannot see how an immersion at any point between 1:00 a.m. and dawn would be safe. In this case, unless the timing works for you to immerse before your flight departs (please write us more details if you think this might be relevant) or there is a mikveh attendant willing to work very late hours for a fee, we would recommend that you delay immersion to the night after your arrival.
We wish you a good trip! Please let us know if we can be of further assistance.