Heating tank with sand substrate

I have a 24x18x18 and am using an UTH with sand substrate. From what i have read, that should be enough for the whole tank, but other than the sand above the UTH, the whole tank is still 70 degrees, when it should be closer to 85. It has been about 3 hours, should i give it more time or go get a heat lamp? also, would 1 suffice or would i have to get 1 for each side?

Sand isn't a very good substrate for ball pythons, and it will absorb a considerable amount of heat due to it's density. You could try switching to newspaper(it's cheap or free) and see if your temps level out better. If the temps still aren't where you want them it would be best to start with one heat lamp and see if that is sufficient. I like to use a 75w or 100w red bulb with a light dimmer, generally I have the light at about 50-60% power, but the dimmer allows me to further customize the bulb to suit my needs.

Sorry, i should have been more specific. i am getting a rosy boa, so from what ive read sand is a decent substrate.

I bought a ceramic heater, and do have a rheostat that i can adjust it with. This should work out for me. /crosses fingers

Oh I'm sorry I just assumed ball python lol. I don't know enough about rosy boas to say anything about substrate, but as far as the heat goes the ceramic heater should work great, just watch it for the first few days until its set up the way you want. :)