In 4e, for a 5 person party the maths works out roughly to one level per 8 or so "encounters" ("encounters" here a notional parcels of level-appropriate XP). Each "encounter" takes around an hour to play, longer if your table is slack and/or if PCs are higher level. So it's roughly a level per 10 to 12 hours of play.
The 4e DMG (p 121) estimated 18 months at 4 to 5 hours per week to get to 30th level: that's around 320-odd hours, which is relatively consistent with my previous paragraph.
My group plays for around 60 hours a year, and have been playing our campaign for around 6 years and are at 28th level. So we're a bit behind the curve (we're old and lazy and normally have young kids with us at our sessions), but not by much.
You can see the original thread here, with some assumptions and discussion around the advancement rate in 5e.
http://www.enworld.org/forum/showthread.php?403665-How-fast-is-the-default-advancement