Custom: you challenge me not to cum until the countdown at the end, this time, with a twist.... You say that people have been cheating (including myself) by either slowing down and not following your instructions, or cumming early and not paying the consequences. So this time i have to start with my legs in the air, with my dick pointed at my mouth. You then tease me mercilessly, trying to make me cum early so we get a facial. If i make it to the end, you give me a nice countdown and i don't have to cum in my mouth. You could do things like suddenly take off your panties/drop your towel/ take off a bra etc to try make me blow early.
