Oh yes, sounds pretty safe to me to get started. Things are not as critial in the beginning anyway, mostly you just don't want to get the ammonia level too high. You can correct things later if you end up having to get fresh tests.
During a fishless cycle especially I often recommend dosing the Prime as high as 1.5x or 2x what the instructions say. This is because water authorities (admittedly not very often, so this is a fairly low risk kind of thing) sometimes overdose the chlorine/chloramine producst they use (their goals are to lower some bacterial count on some distant set of pipes, things like that.) So the way you could view this is that since counting out 33 drops of Prime (or some lesser amount obviously) every time you change water would be a big pain, you will want to find some other delivery device (such as a syringe that has milliliter markings from the pharmacy or even a teaspoon or something) and this frees you up to pick some larger amount (somewhere very roughly halfway between 1.0(what they tell you) and 2x of that) that happens to be very easy to repeat.
The "bacterial growing soup" (that's what I call it to remind myself that during fishless cycling I'm optimizing it for bacteria and that its only misleading to think about its parameters with respect to my future fish - all characteristics of it are about the bacteria) needs to be warm and the current optimal number we're working with is 84F/29C.
~~waterdrop~~
