Applying QUICK-SETTING CEMENNT to the bottom of where the door casing goes

Please watch the entire series. These videos are short and to the point.
I found myself in a jam (pun intended) when I removed the old threshold, I noticed that there was just a stone and at that the stone was quite uneven. This would not be a good foundation for the new door casing to rest on.
What was I to do when I had very little time in my day to get this door completely installed?
The answer is a product called QUICK-SETTING CEMENT. See link below.
I am not sponsored by Loewes or quick krete
www.lowes.com/...
Please watch the entire series. These videos are short and to the point.