Thanks for the response Kat & Uncle, that formula works very nicely, I don't think I ever would have come up with anything like that.
But as is often the way with such things, having tussled with the problem for a while and then slept on it, I came up with a solution.
=RANDBETWEEN(37500,87500)/100000
Your Uncles formula is better though because it formats the cell to show a time, whereas mine doesn't.
Thank you both. : )