They've made leveling quite a bit faster. It takes me only a few hours of gameplay, and I'm a very lightweight player. I don't min/max, I don't optimize for the absolute best numbers, I just play. If you're a serious player who knows how to get all the best out of your ship and crew, you'll probably do it even faster than I do.
Many people think they've made it too easy, but I like it as it is.
Before they rebalanced the way leveling works, it took me about two weeks to get from Commander 30 to Commander 36. I'm a slow player who stops to enjoy the scenery and screw around in Earth Space Dock.
However, since I've come back around Jan 12th, I'm about 1 exploration mission shy of Rear Admiral 40. So it won't take you long. Especially if you do the story missions, which I skipped out on because I don't like high yield plasma torpedoes.
If you jump into the 'red alert' Borg incursions if there happens to be one in your sector block, that will kick you up quite a bit. I've quite literally advanced a character an entire grade simply due to those things.
Personally, I think leveling in this game is too easy, but lacking more content, it's probably best to allow people to get to VA as quick as possible. However that's a discussion for another thread (which I am sure has been discussed, likely ad nausium).
Its taken me about a week (with lots of wifi issues) to get from lieutenant 1 to commander 29 (its allot harder i made ltcmd one day and then commander the next but the rest has all been as a commander and i should have made it but had several connectivity issues