Nothing concrete - only that a player may not "unduly delay" play, and if the player does, he incurs a two-stroke penalty in stroke play or loss of hole in match play (see Rule 6-7).
What constitutes an "undue delay"? The rules don't say.
How long does a golfer have to play an individual shot? The rules don't address this at all. How long to complete a round? Again, the rules do not address it.
Although the rulebook makes no ruling on the issue, rules committees do. That's why you sometimes see Tour players being penalized for slow play.
The rules committee for a golf club or competition may set any time limit it wishes to encourage a faster pace of play. In competition, you should always know the pace-of-play regulations in effect before beginning play (or better yet, play quickly enough that you never have to worry about it).
There are some time limits in the rules, however. For example, you have five minutes to search for a ball before it must be declared lost; if a putt hangs on the lip of the cup, you have 10 seconds following your walk to the cup to wait for the putt to fall.
