No, definitely not. Evolution does not do anything to your EVs and especially not your IVs, which never change under any circumstance. The only thing that evolution does is change the Pokemon's base stats. So it does not matter what level you evolve it at in any way; assuming it gets the same amount of EVs from Pokemon it beats, there will be no difference in Milotic's stats at level 100 if you evolved it at level 10 and not level 50.
