How much time is needed to put into this game
How fast do you want to get to level 90?
And what kind of guild do you want to be in?
If you're talking about getting to level 90 really quickly - you'll have to spend a huge amount of time on this game for a month or so, and make your wife hate you.
And if you want to go into one of the usual max-level "let's go on level 90 raids" guilds that are all over the place, then expect to spend a lot of additional time at level 90 grinding the optimal gear from heroic dungeons - just to qualify to go on 10 or 20 man raids.
And keep in mind that a typical guild raiding session happens two or three evenings a week, and is about 2 or 3 hours per session.
But you don't have to go for a hardcore raiding guild either.
One of my alts is in a casual guild with about 300 members or something - and they are really laid-back about everything. Mainly it's just a place for people to hang out in guild-chat, ask for advice about the game ("how do I complete quest A - I'm stuck") trade favors, or arrange to trade with other members for needed crafting materials. Some group members raid, but mostly they just hang out. In that guild, no one cares how long I'm on the game during the week.
To be honest, I think I'd recommend a more casual guild to you to start out. The raiding guilds can be a one-way ticket to burnout and sleeping on the couch if you don't work your way up to them gradually.
Just make sure the guild master is OK with the way you want to play when you join up. This character - Rhymetha - is in a traditional raiding guild, but they're laid back enough that they don't require me to raid at all (which is good, because I'm not geared for full raiding anyway). Mostly, they're just available if I need to find out some information, or ask someone to help me do a run through old level 60 or 70 raid instances for transmog gear.
Leveling and gearing up will just take you longer. Rep grinds will take more time since you will probably not do a full slate of dailies every night.
You CAN do casual progression raiding (killing heroic raid bosses) on 2 hours a night, but you may have difficulty finding a group. (My old raid team raided 6 hours a week: 3 hours a night/2 days a week, and killed most of the heroic raid bosses in Cataclysm.) And spending all your in-game time raiding can burn you out.
Casual PvP generally does not take a lot of time (random battlegrounds usually take under a half hour per, and arena matches rarely last more than about 5 minutes each unless you end in some sort of healer vs. healer or tank vs. tank stand off where nobody dies), and if you enjoy PvP, it'll just be that leveling to 90 will be slow for you.
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