You can just set the heater at the desired tempersture. and go ahead and put him in and the heat will go up gradually. Or, if you want to wait until the water gets to the desired temperature then you can float him in his cup for awhile to get him acclimated. I hope this helps.
hey I jus need some information please. I jus got my betta last monday. of course I was told that a 1 gallon bowl wit no heater was fine! After finding this site I seen otherwise. So I am planning on getting a 10 gallon tank for him. I was wondering about how 2 do the heater. Should I have the tank set 2 what it is now and jus raise the heater a lil at a time? I dnt want it 2 b a complete shock 2 him. Bob always makes the little bubbles on 1 side of the tank and I read that means he is happy...but I want 2 keep him for a long time so I want 2 make sure I do things right! sorry so long!