I know it's hard and I'm still not nearly as proficient as I should be. But it's only a glance to get a number in your head. But trust me, the first time the clock runs too long and you step with a confident "there should be 2:15 on clock" your stock will rise.

And it's doubly important when working with a shot clock.

Thank God We Had A Well Mannered Coach ...
 

Happened to me in a girls varsity game a few years ago. Three point shot near the end of the second period. I'm the trail. Ball bangs onto the rim and bounces high into the air. I figure that there's not going to be any basket interference in a girls game, so I peak at the clock in case there's a rebounding foul. While I'm "clock-glancing", and while my partner is keeping his eyes down looking for rebounding fouls, the ball hits the cable above the basket. Of course everyone sees it hit except me and my partner. I turn to see the ball going in the basket, which is followed by the buzzer sounding. I count the three point goal. My worst call of that year.

Of course I topped that worst call with a "worser" call the following year, a fist violation. But that's a story for another night. Sleep tight.