That is one almighty impossible to answer question.
First of all that depends on the season. Senators aren't in Rome at all times, summer is a good time to be on the farm to avoid the heat, IIRC autumn is election season (while that matters). Summer is also campaigning season for the early Republic and generally the time you can safely travel. Winter is when everybody who is anybody is likely to actually be in Rome.
Then the kind of day it was. Is it a dies fastus (a day when courts may sit) or a dies comitialis (a day when the popular assembly may meet), a dies nefastus (when no assemblies may meet and courts *should* not sit) or a dies nefastus publicus (good question - probably a day on which no official business at all other thasn religious acts was to take place). If he is on a court, his schedule is full. If notm he may still hae to attend other functions. If the Senate sits in session, he has to go there.
Very (very, very) generally speaking, your typical Roman mover and shaker would rise early, but not extremely so. He would meet his clients in the morning, distribute food and largesse, shake hands, talk small and listen to their problems. If he was a junior senator, he may have to go visit a patron of his own, thus rise even earlier. The lower down the food chain, the earlier out of bed. This tradition was not religiously followed, and not every day, but it was still very much alive in Principate times.
After rising, washing, possibly changing (some Romans slept in their underwear and changing it daily was not regarded a necessity), dressing and having a light breakfast, off to work. Accompanied by his servant(s), possibly friends or proteges, and - if the occasion called for it - a number of clients, he would go to do his day's work. That could be sitting on the panel of a court or presiding one, attending a Senate session, representing someone in court, attending the Emperor (once there was one), electioneering, or running his private business (mostly agribusiness, real-estate, moneylending or slave-hire, since senators were barred from trade). If he holds office, there will be other duties, and he may have to organise games or other entertainment as well as fulfil religious duties. Not all at the same time, though.
Unless there is some kind of crisis, work is supposed to be over early, after which he could be off to enjoy a leisurely afternoon. In theory. In practice, there will be clients, attention-seekers and people to meet on busioness or socially as well as the attractions of the bath, the palaestra, the libraries, theatre or (if it's on) the circus or arena. If a major game is laid on, a senator pretty much would have to be seen to be present or risk snubbing the organiser (which, in the case of some emperors, could be hazardous to your health, but generally would be rude).
In the evening, chances are good there will be a dinner party. The Roman upper crust held banquets with mind-numbing regularity and again, if you didn't attend and invite regularly you risked dropping out of the loop. No firm statistics exiost, but a powerbroker of the first order could have invitations almost every day of the week. A less semnior figure might well still expect to dine out or entertain every second or third day. This phenomenon is on the rise from the Middle Republic (at least) well into the Principate. I would counsel against images of lucullan orgies - Pliny describes a very frugal meal in an invitation, and while he stresses the fact, it can hardly be considered implausible (and Pliny was not a poor man even by the Senate's standards). Your typical dinner would feature plenty of good-quality food followed by wine and conversation, the latter probably the most important thing. Small trinkets would be given as gifts. The whole thing was more or less the equivalent of the 'cocktail circuit'. Only the very wealthy and/or tasteless rivalled in conspicuous ostentation, though a certain standard was expected.
Then off too bed and out the next morning, early. Power hath its price.
Der Kessel ist voll Bärks!
Volker Bach