I have a problem with time

It seems that the clock is my worst enemy, especially now that I'm playing against people of equal or higher strength.  If I don't spend enough time in the opening and middlegame to make strong moves, then I end up losing.  If I spend too much time then even if I'm up in the endgame I'll lose on time as long as the opponent can defend long enough.

Any tips on how to get faster?  Is speed in analyzing positions just something that comes with time in games?  Or should I be spending more time studying positions in preparation for games?  Any tips greatly appreciated!

You might try playing... shorter time controls. It helps to be able to form a quick, rough judgment when you need to, although playing too many short games can get you in the habit of playing atrocious moves that won't go unpunished in long play. But being able to make a move because it feels right, when you have no time to calculate, is a useful skill that you won't lose.

Studying, of course, will also help. If you are spending time thinking in the endgame that is probably the best place to improve rapidly, but it sounds like it is the middle-game that takes away most of your time. Studying is not as effective here, since there are so many possible positions- just play and play and play and you'll get better.

Check on Dan Heisman's Move Triggers novice nook. 

It appears you are hitting and ignoring trigger #2, i.e. not playing what is objectively the best move you've found, when your budget of time per move is up.

I've seen a lot of players getting better suddenly decide to strive for perfection on each move  by long deep thinks. This is good if the position warrants it but more often than not, this backfires because:

- you are not going to get significant gains by spending any  time more than it is required to visualize all forcing lines clearly AND till quiescence. Good players will calculate forcing lines ... you should too... but don't dawdle when there's nothing to calculate.

- You end up worrying too much on things that stronger players don't weigh as a concern.

- Unless the position is highly analytical, you are committing time-control suicide by deep-thinking through them.  ( such as the early in the openings or positions where analysis won't tell you much ) When this happens, most players are really being inefficient about what they're even thinking about!

You might as well use your evaluation skills and and just play your  best "tactically safe" move  when trigger #2 kicks in.

A good thumb rule for trigger #2:

For e.g.  if your game is  60 minutes =>   1.5 minutes a move, assuming an average 40 moves per game.  That's your budget for trigger #2.

Assuming that a set of your moves are trivial recaptures and blitz-ed out opening moves that occur in seconds,  you have some leeway to go beyond this budget in certain positions. Give yourself 2-3 X budget for critical positions that are highly analytical...i.e. about 5 minutes.   For everything else, take 1.5 minutes and no more (trigger #2) or quicker if you are confident (trigger #1)

Note:If you think this is a deciding "Win or Lose" point in the game, take as long as you need to ... but remember that after this move, you should be able to win on autopilot. If you are winning a piece (or even a Queen) through a tactic,  the winning technique is easier ... but if you burned 25% of your clock for a pawn, you might have a tougher time trying to convert the point.

Pace yourself with a clock or write down the time taken per move and practice until you get decent at this.  As you indicated, speed at evaluation + analysis gets better with experience.  But bad time management doesn't!

Remember, how often do you get into a situation where you tell yourself "Oh, I thought for 3 minutes on that position and played the 3rd best move I could, if only I thought for 6 minutes, I'd have unlocked the key to this position's hidden secrets and won the game". (yeah, right :) )

What's more realistic and likely is the popular whine "Oh, I played so well for the first 30 moves but I got into time pressure so I blundered".