Having been to "nites" where a DJ has had a couple of hours to himself before the next DJ, I thought he'd lost the plot after about 1h20m as it became quite clear it was just a matter of "playing stuff" to finish his 2hrs rather than keep the floor moving.... remember you can "overdo" or "outstay" when up there ....
As for requests.... it's quite simple really.... you "slot" them in or be honest and say "if I can, if not ask a later DJ".... or of course there's that old chestnut "I ain't got it with me" .... and how many times do you hear a DJ say "requested sounds of blah blah" only to know NO ONE has been up for an age .... that's the line to make peeps think the next tune "must be good as it's been asked for" which always makes me PMSL ....
One hour is approx 22-25 tunes, IMO, and that's just about right to "move on" from the guy/gal before.... to then leave the guy/gal following to "move on again".... it's not about self promotion after all is it.... it's about doing the business....
As for "modern".... you cut your cloth accordingly as they say.... make the set work however long the records are.... but I'll leave further comments on that one to PeteS ....