The cell divisions won't all happen at the same time, particularly after the first few.

If you consider what happens - the first cell splits into two cells.

Then each of those two cells splits to form a 4 cell embryo. If one of those 4 cells splits earlier than the rest, you will end up with 5 cells and it's still perfectly ok.

I've only ever transferred blastocysts (too many cells to count) and one day three embryo (8+ cells) so I can't really comment for sure on whether that's good or not for a day 2, but it's certainly along the way to becoming an 8 cell on day 3 so I'd imagine that it's ok.

BW