Came across two sentences w/o for and became curious if it's correct and appropriate.
They have been together __ four years.
I have been waiting __ two hours, can't believe she stood me up.
Came across two sentences w/o for and became curious if it's correct and appropriate.
They have been together __ four years.
I have been waiting __ two hours, can't believe she stood me up.
Yes, it is very common.
The right side of this NGram shows some of the top hits from books including and excluding for:
Either way, it will be understood.