Very carefully. Never ever plan a block over 8 hours, usually between 2 and 6. And practice. It's not something you can learn easily, you have to adapt for your

Very carefully. Never ever plan a block over 8 hours, usually between 2 and 6. And practice. It's not something you can learn easily, you have to adapt for your own brain. People say they double their estimates, but I find it no longer necessary, I usually hit the time 1 hour +/-.