Can I warm up a cold cup of a tea and drink it hours later ?

Yes, you can, assuming it's not two weeks old or more.

yes its okay to do that

Yes, you can if you want to.

Do not expect the tea to taste fresh or become piping hot. Consume it when it is lukewarm. For the sake of your digestive health, do not reheat teas exposed to room temperature for more than four hours.

Yes, but it would probably taste 'odd', I'd throw it and make a fresh cup!

NO! You will get beri-beri and die. Geeze, what is Wrong with you kids today? 

Yes.  Iced tea is basically cooled tea with ice added.

If you are going to keep tea for more than a few hours, it should go in the fridge, otherwise it will grow mold.

Yes it's fine.   Tea is just flavored water.  There is nothing in it that will go bad even in a day or two.

It's a good idea to store beverages in covered containers so they don't get dirty, collect bugs, etc. 

Yes, you can put it in the microwave for 45 seconds.

Assuming you are at home where there's no danger someone slipped some substance into your drink, reheating and drinking your tea is harmless. 

But when you go out to parties or clubs, be safe with your drinks. Keep a drink in your hand, and don't drink any more of it if you went off and left it on the table even for a minute.