Assuming you're wanting to survey an entire sector at a time, The Imperial Fringe (Deluxe Traveller introductory adventure, reprinted in Double Adventures 1-6+) does something similar and states that, with jumping, one world/system can be surveyed every two weeks (for this, jump rating doesn't really matter, as long as it's good enough to get from one system to another - jump 3 might do, but jump 4 would be handy for the occasional gap). That's for the already-known worlds of the Spinward Marches. Still, given this as a base, and given average (50%) map density, there are 1,296 hexes per sector, giving 648 with planets to be explored (the Spinward Marches has only 440 worlds). Thus, a quickie survey of a typical sector would take about 1,296 weeks or 24.9 years. Spending more time surveying would increase the overall time (two weeks in-system would extend the time to 1,944 weeks or 37.3 years; taking longer would increase the time proportionally, keeping in mind the week needed for jumping). So, in 250 years, you could quickly survey 10 sectors, or more thoroughly survey 6.7 sectors, with a single ship working at it. This doesn't include time for maintenance or replacement of crew, however.
