30 minutes later can be expressed as "in thirty minutes" or "after thirty minutes".
This phrase originates from the standard way of measuring time in minutes and expressing a certain amount of time passing by using "in" or "after".
Example sentences in Engpsh with Chinese translations:
I'll meet you in thirty minutes at the park. (我会在公园里等你，30分钟以后)
After thirty minutes, the movie will start. (电影30分钟以后开始)