Shouldn't this be private?

As I’m starting to learn more about private/public, I came across this method in the callback section.

Shouldn’t this method be hidden from public header " -(NSString *) lastTimeString " since ivar lastTime could be at a state where it hasn’t been instantiated or set yet ?

If I do decide to declare it as part of public header, shouldn’t we have some check in place ?

I apologize if question is very elementary but I just wanted to learn it to right way.

Thank you for your help.

You are right - hide details wherever you can.