About round-world, I tend to specialise in it nowadays!

I found both pottering around with short trips near home, and cruising in the stratosphere in a jet, equally boring after a while. So one day I tried the 'MacRobertson Race, England to Australia' scenario in the DH88 Comet. Nearly killed me (the default aeroplane doesn't have an autopilot) but I got to Melbourne - and then, on impulse, took it all the way round.
The very best thing about that trip, of course, was that I 'stuck to the rules' and stayed below oxygen height (maximum 12,000 feet or so) - which meant that I had to thread my way through the Rockies and go round the Alps. That made for terrific scenery and lots of challenging flying, and I was 'hooked' for good.
Since then I've taken almost all the default props round - including the Cessna and the Dakota - and a lot of downloads. My current trip is in a De Havilland Leopard Moth (1930 three-seater cabin type, far ahead of its time) - I've just finished threading my way round the mountains of Papua New Guinea and am setting up to land at Jackson's, Port Moresby. The best thing about using short-range types (the Leopard Moth, for example, only has a range of 900-1150 miles, depending on winds) is that you have to plan your routes carefully, and often have to land at airports that are less than fully equipped, because there is nothing else available.
As to time, the last thing I would do is just leave the computer running while I do other things - where's the fun of simming if you're not even THERE? So on the long stretches (especially over oceans) I make judicious use of 'accelerated time.' Make it a rule, though, only to use it when cruising, always handling the initial climb to height and the letdown myself in normal time. And use VOR-to-VOR navigation or 'dead reckoning' for navigation, never GPS hold. Also, of course, AT won't work properly in bad weather. I find that that's a fair compromise between realism and having fun.
Wrote it up once in a tute which has some screenshots to whet your appetite - available here ('FS2004 Round The World In A Prop,' halfway down. Fair warning though, once you're an addict you'll never be able to give RW up!:-
http://www.simviation.com/simviation/static.php?ID=151&page=10