I think the temperatures for your hognoses are too low now as it is. In many parts of their range, temperatures don't dip below 90° at night. I have always been a strong believer in providing warm basking areas for captive herps, and I have seen a lot of problems associated with too weak of a heat lamp. Reptiles rely on "behavioral fevers", what if your hognose became sick with a fungal infection or internal parasites? It would not be able to achieve the necessary body temperature to fight off the infections.
Under tank heaters are not appropriate for hognoses since they burrow into the ground to escape high heat.
I recommend getting a heat lamp on the tank now, and make sure that at least one small portion of the area the heat lamp hits gets up to 95°.
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"I know the human being and fish can coexist peacefully."
Governor George W. Bush, Jr.
"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Calvin and Hobbes (Scientific Progress Goes 'Boink', 1991)