401K Hardship Withdrawal

I have an employee that took out a $25k hardship withdrawal. He has not cashed the check yet; however, he found out he does not need as much as he originally thought. Is he able to A) cash the check and return a portion back to the plan B) return the entire uncashed check and take out a lesser amount of hardship? I am unsure on the rules on this. I thought at one point I saw there was a set number of days that the funds could be returned without tax or penalty. Thank you!