READY
READY
Ninety minutes is the long block deep work talks about most, and it is the length a lecture, a football match and a full rehearsal happen to share. The usual explanation is that it matches a natural ninety minute swing in alertness, the one that structures sleep and is said to carry on while you are awake. That idea is popular rather than settled and the evidence for it during waking hours is thin, so treat ninety as a working choice rather than as a number your body is keeping.
It is a poor choice for a task you are avoiding and a good one for a task you have already started. A block spends its opening getting back into the work, and the longer the block the smaller a share that opening takes. That is the whole case for a long one.
The tip: protect the beginning, not the end. Put the phone in another room and close the mail client before you start, because the failure mode of a long block is not running out of energy at minute eighty; it is being pulled out at minute twelve and never getting back in.
When it rings, stop properly: fifteen or twenty minutes away from the screen rather than a scroll at the same desk. A block this long earns a real break, and getting up is what makes it one.
The usual answer is a ninety minute cycle in alertness carried over from sleep, which is a popular idea rather than an established one. The practical answer is that a longer block gives the opening a smaller share of the session, and ninety still fits into a day twice.
For a task you have not started, usually yes. For one already in progress, more of the block is work rather than warm-up, which is the reason to pick a long one.
Yes, and a real one: fifteen to twenty minutes away from the screen. Skipping it turns the next block into a continuation of this one, which is not what the length is for.