You may be surprised, but "זְמַן" is the word we need when we say... "for a while"!
How do we say something like
"I have been working here for a while, and I still haven't gotten any promotion..." or
"I am waiting for you for a while already!"
We say -
!אֲנִי עוֹבֵד(ת) פֹּה הַרְבֵּה זְמַן וַעֲדַיִן לֹא קִבַּלְתִּי שׁוּם קִדּוּם
!אֲנִי מְחַכֶּה לְךָ כְּבָר הַרְבֵּה זְמַן
No other way to say it, this simple!
Now, if you know how to say "for a while" you may be wondering, then, how to say...