Soil Heating temperature Advice required

[murihikukid]

Hi..Today I put soil in my Stainless drums and switched the panel heater on which is located (on stilts) in the bottom of a freezer shell .....Due to my having no fitting for a cable to my STC 1000 Thermostat I just powered it so I could get a Temperature reading and Switched the panel heater on....I watched the temperature rise to round 45F and unplugged the heater and watched the temperature fall and repeated this several times....
Tomorrow I should have the Thermostat up and controling the heater.....Now I am only guessing but it will take several days of continuous warming to get the soil to the required temperature...so as I can transplant my plants..

So heres what I need advice on...What is the correct soil temperature for tomatoes cause I have seen a wide variance in articles....and I would not heat up to 80 degrees F as I have seen .. I would sooner go for a lower number like 60 to 70 .....and am I right to think that the air heat will take several days to actually warm the soil...Again I have read 100degrees F air temperature equals 75F soil temperature ....
Regards Ron ..NZ