Hello and welcome!
First off I want to say props to you for seeking the right information out on the proper care of your snake. Your taking a great step by doing so..Now onto the answer..
I would say for now don't use any heat mat if it's not being controlled by a proper rheostat or thermostat..Your snake will be okay for a little while in 70 degree weather, but it is important to get the heat pad and proper temp. control unit soon..You said you already ordered the heat mat (zoomed is a great choice!)..Now ya just need the temp control unit..Many different members on here go with different things..some like myself use thermostats that you can buy at some pet stores or even order online..I ordered mine (Repti-Therm500R) from "Reptilesupply.com"..for a really good price..and it can control 2 heat mats at once..so it's very handy :0)..other members use rheostats and even light dimmers that they buy at various stores or even make their own (though from what I hear..rheostats take a little more adjusting constantly then thermostats do..)..So you definitely have some options to choose from..I know you can buy a good thermostat online and as for a dimmer..I would suggest looking that up in the search engine this forum provides..you can search "dimmer" or even "rheostat" to see what other people have done..Sorry I can't really help ya much on that subject..lol..
When ya do get a temp. control unit, just so you know, the warm side of a snake tank is usually good at anywhere from 83 to 86 degrees..Just in case you were wondering how warm it should be..
I would definitely say not to use the heat mat before you get a temp control unit as those things can get to over 100 in a matter of an hour or 2..and can cause serious harm and stress to your snake...
Much luck to ya and hope to see ya around :0)