New Pueblan Milk Owner - basking light vs heating pad?

[Ilikeplants]

Hello all, new snake owner here. I got a 2 year old Pueblan Milk on Friday. He is I have him in 20L with an inch of bark substrate, two log hides on either end. The reptile store gave me a basking light, which makes the substrate about 90 when I have it on. I keep it on for about 12-13 hours from 7AM to 8PM until I can get a timer. My apartment is only set to 70 degrees at night, should I be using a heating pad, and should I be using said heating pad besides the basking light? I read they are nocturnal so pad is better than a light. I ordered a 8" x 7" heating pad. Thanks!