Ah yes, those first few sore footsteps of the day. You may be interested in reading this thread
One of the ideas discussed was that as your foot is getting stronger and more flexible,
the muscles and other tissue knit back together during the night after a hard day's work,
and in the morning, you undo some of that work as you put weight back onto the feet.
I had it for about 3-4 months, interestingly it wasn't a problem in the very first month I had my VFFs.
If the ache goes away after a few steps then it shouldn't be a problem, but its always good to listen to your body.