Days till event countdown. UNO

I am making a countdown clock for days till event. I was going to program it by counting down seconds 86400 = 1 day. Is this the best way to do this? I am new to arduino so I figured I might be missing something simple. I would appreciate in advice.

You want a real time clock (RTC) module. Uno can be off 3+ minutes a day.

The RTC can be used different ways so you get to find out which you like best.