You can revert files instead of using "u" to undo. It is not 100% accurate but can be useful if you've made a big mistake and need to revert an entire file back a rough number of minutes.
This creates a branch of the file you are editing.
Out of insert mode user the following commands:
:earlier (number of minutes)m
:later (number of minutes)m
You can also set more specific times by substituting m with the following:
s = seconds
m = minutes
h = hours
d = days