Start almost embarrassingly small so the habit sticks. Choose the same 45-minute slot each day, ideally in the morning before the day fills up. Write down the single thing you want to accomplish before you start the timer.
Then remove friction rather than relying on willpower: phone in another room, notifications off, one tab open. When your mind wanders, just note where you were and return, without judging yourself. Repeat it daily and let the streak build.