The change won't be that great but you will probably have a lower FSH on CD 2 (which is always encouraging) .....so I would go for that and then just start the meds on CD 3 when they get back to you.
If you are doing it to see if it's a good month, or if you are doing it to be more encouraged emotionally because you want to go forward either way. Day 2 fsh could be lower and therefore more encouraging. On the other hand in my personal experience AFC tends to be lower early on and maybe gain a digit or two as the month goes on.
I think both days are fine though. I personally prefer to go on a month where numbers are on the better side. If numbers are worse than usual then I prefer to wait it out, but that is just me. A lot of people (RE's included) do not agree.