You can get total number of commits through a time period with two different ways
First way
Using since and before - since take the start date and before take the end date that you want to get commit from it.
git rev-list --count HEAD --since="Dec 1 2021" --before="Jan 3 2022"
Second way
Get the total commit by using [second - hour - day - week - month - year]
Get the total commits by second
git rev-list --count HEAD --since=600.second
Get the total commits by minute
git rev-list --count HEAD --since=30.minute
Get the total commits by day
git rev-list --count HEAD --since=28.day
Get the total commits by week
git rev-list --count HEAD --since=4.week
Get the total commits by month
git rev-list --count HEAD --since=1.month
Get the total commits by year
git rev-list --count HEAD --since=2.year