Gambling indeed takes a lot of time especially when you did put a lot of money to it but only bet in small denominations. The only time that you are actually going to stop gambling for the day is when you have lost all of your money in the gambling site or something urgent comes up. The latter is always not the case, obviously. As your addiction grows and the more messed up your brain becomes, the more you are going to be less focused on the things that you are doing. This means that you might be gambling right now but while you are gambling you are going to watch the TV while doing another activity. With that, you are constantly distracted and the time for you to lose all those money in gambling will even be prolonged. The more you get addicted to it, the more time you'd lose for work and school due to gambling.

And yes, I did lose time for work and school because of gambling and I think everyone does. Gambling takes some of your time and any distraction is going to make you lose time for work/school.