Add an hour to system time and save that value?

Unity Engine
1

My game saves the system time when the game starts, calculates an end time 1 hour later than the start time, then checks to make sure the current time isn’t greater than the end time (if it is - the game ends).

I need help programming how to add an hour to the start time and checking the current time isn’t greater than the end time.

I get the system time with:
currentTime = System.DateTime.Now;

How do I add an hour to this and store the value?
THX a mil!

2 
DateTime.Now.AddHours(1)
3

Thanks! Part II - How do I get just the minute value from TimeSpan ts below?

// get time app was closed and determine elapsed time

long closeTime = long.Parse(PlayerPrefs.GetString(“olddate”));
DateTime oldDate = DateTime.FromBinary(closeTime);

TimeSpan ts = currTime - oldDate;

4 
ts.Minutes;