Is there a way I can get my water heater from tripping my oil furnace
to go on all night to keep the reserve tank hot? It's using up about
1.4 gallons a day this summer and all we use the hot water for is
taking showers -about 1 per day, and washing dishes - every 3 days. I
think it's using too much oil just to keep the water hot and I'd like
to be able to have it turn off from 11pm to 6am every day so I don't
waste so much oil while I sleep.

If I cannot do this myself who do I call to get it fixed. Will any
furnace specialist be able to fix it or do I need to contact someone
with experience with tankless systems?

Just for clarification my tankless system is not the square box on the
wall, it's a mini tank connected to the furnace about the size of tank
used to power your standard outdoor gas grill.