I've found it useful to think about managing time just like managing money. This is beneficial because the concept of budgeting — in the finance world — is commonplace. It's also a simple and effective mental model.
We don't always think about time as money, but it's genuinely our most-finite resource. Each day slips by, and if you don't use your time wisely, you will have none left — just like money. When we go to the grocery store, we need to know we have money before we spend it. When we plan our day, we need to make sure our time is budgeted appropriately.
There's a budgeting philosophy where "every dollar has a job," meaning you assign an explicit "job" for every dollar you take in. For example, if I have $1,000, then I need to give each $1 of that $1,000 a "job" to do. $100 for internet, $200 for gas, etc.
Managing your time is no different.
Look at your calendar right now. You'll most likely see some all-day events or reminders, meetings you have, and (hopefully) some free spaces or blocks. Those free spaces are time, and you need to give each block a job — what am I going to accomplish in this time? How am I going to use my time wisely?
If we think about time this way, it can help us schedule and prioritize the things we do.