I remember them finishing at about 10:30-10:45 at most shows I have seen in the UK.

Judge it by what time they come on stage. If they come on at anything after 8:30 then you are in for a short set list, if they are on at 8:00 then a longer set is a possiblity.

I believe there is no real support band at Southampton, apart from a local band, will this mean the band come on earlier and give more??? Who knows, we will have to wait and see.

Manchester and London seem to get good shows so I think you will have a great time.