As long as your cold side temps don't drop below mid 70s ( 24-26c ) I would simply use the heat mat to maintain a hot spot throughout the night and then in the morning turn the lamp back on to raise ambients for the day.
Although I do believe there are night lamps you can use that will allow you to view your snake when they are most active without bothering them, I personally have no experience with lamps though
Edit: I don't believe it would have any affect on your snake if you switched hot sides from morning to night but I would suggest maintain the 88-90 f ( 31-32c ) hotspot with the heat mat and then raise ambients of the entire cage to around 80f (27c) with the heat lamp.
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