Hourly Check Ins + Write It Down

Set a timer that goes off on the hour. When it chimes, write down what you did during the last hour (I do this on my Google calendar and I like to color code). Then, restart. It's easy to get distracted/lose track of time, so the hourly check-ins keep you moving along and time entries keep you honest. If you have to write down that you spent the last hour online shopping, at least you are accountable and it doesn't inadvertently become three hours.