We have to contend with interruptions, meetings, etc. So, instead of scheduling the entire three-hour project for tomorrow, schedule a small bite, a step or two that might take 20 or 30 minutes. Then put the next step on the next day's To Do list and the next step after that on that next day's list, etc. It may take several days, but you will get that elephant eaten up, one bite at a time. Plan around interruptions.
Interruptions tend to occur in identifiable patterns.
I get most of my interruptions early in the day versus later in the day. I get most of my interruptions early in the week versus later in the week. So, if I plan a big project first thing Monday morning, I'm creating stress because as soon as I begin, interruptions arrive and re-focus my attention causing me to procrastinate what I really wanted to do. It is so much easier swimming downstream with the current rather than bucking the tide. Therefore, I plan those larger projects for later in the day and later in the week when I tend to get fewer interruptions.