Fastest ones on the hour from Waterloo, next fastest (five mins slower into Fratton) on the half hour. The slow ones are at a quarter past the hour and a quarter to the hour. This doesn't include the long-way-round services via Basingstoke and Winchester (obviously not an option for you and
@rvw), which are one an hour and take two hours to get to Fratton.
For what it's worth, if anyone's thinking of saving some money and getting the Southern service out of Victoria, I'd warn that there's only two bike spaces (well, there are four at Victoria, but the back half of the train goes to Bognor so you don't want to use that set), and it takes two hours to get to Fratton. It's handy at times but I'd avoid it on this occasion. Also the cheapest tickets are 'Southern only' so you can't switch to SWT services if there's a problem on the line.