...and what the quality is. It doesn't make sense to wait for five days if you only have a few embryos that look decent. You want to transfer them as soon as possible, and not risk having them compromised by a longer wait. If you have a huge number of very good embryos, then waiting for five days would make sense, as then you can pick out the very best ones for transfer.
In my case, cycling in South Africa where they do a "low stim" approach, it's usually day three... I had only four embryos, and only two that were really good. Of course we transferred on day three (and I was successful with a singleton).