Metatime is the concept, often portrayed on television or other media, that the protagonists have their own functional timeline irrespective of any timelines or changes occurring around them. However there is a limit to the metatime and it does start to get fuzzy around the edges when it used up:
Metatime is recorded on the collective Playbook and belongs exclusively to the PCs. It has three statistics - Width, Length and Lag. There are additional bonuses you can add to your collective Playbook that will give you more utilities with Metatime as well (such as extending it temporarily to passengers on your Timeship).
If you exceed the Length, you accrue a Completion point as well as suffering from various “time fixing itself” changes as the Grandfather sees fit.
This a list of official BBC media that uses these concepts as a part of the story: