Usage of "until after" vs. "until" vs. "till after" vs. "till"
Solution 1:
Here, until would mean the registration happens at the end of specified time period, possibly sometime after. Until after put more emphasis on the fact that the registration could happen anytime after the end of the period. Very similar meanings, but slightly different. Compare:
I'll be here until 8pm. (I'm leaving at 8pm)
I'll be here until after 8pm. (I'm leaving at some unspecified time after 8pm)
Till, or 'til, are just shortened, less formal versions of until. Till is generally the preferred form of the two.