Org provides two types of timers. There is a relative timer that counts up, which can be useful when taking notes during, for example, a meeting or a video viewing. There is also a countdown timer.
The relative and countdown are started with separate commands.
Start or reset the relative timer. By default, the timer is set to 0. When called with a C-u prefix, prompt the user for a starting offset. The prompt will default to a timer string at point (if any), providing a convenient way to restart taking notes after a break in the process. When called with a double prefix argument C-u C-u, change all timer strings in the active region by a certain amount. This can be used to fix timer strings if the timer was not started at exactly the right moment.
Start a countdown timer. The user is prompted for a duration.
org-timer-default-timer sets the default countdown value. Giving
a numeric prefix argument overrides this default value. This
command is available as ; in agenda buffers.
Once started, relative and countdown timers are controlled with the same commands.
Insert a relative time into the buffer. The first time you use this, the timer starts. Using a prefix argument restarts it.
Insert a description list item with the current relative time. With a prefix argument, first reset the timer to 0.
Once the timer list is started, you can also use M-RET to insert new timer items.
Pause the timer, or continue it if it is already paused.
Stop the timer. After this, you can only start a new timer, not continue the old one. This command also removes the timer from the mode line.