Na twee uur bel ik je terug = After two ours I'll call you back
except that "after two (h)ours doesn't exist. After 2 (because you know that everyone is talking about time, not days or anything else) or after 2 O'clock. When you have lived in England for a while you will understand the difference between the two.
Unless of course, you mean "I'll call you back in a couple of hours, or more, from now." (whatever the time now is).
 there are special occasions when you can say "after two hours I'll call you back but these don't enter into this thread; but then this thread is very academic and divorced from real everyday situations