If after 30 seconds you don't know how to conceptually solve it, like you just have no idea - skip the question (obviously after having eliminated choices which are obviously wrong...this may not be possible because you have no idea how to answer the question)

If at the 1 minute mark, you know it'll take you another 3-4 minutes to brute force the answer, you're doing it the wrong way. There has to be a quicker way.

At the 2 minute mark is when you absolutely must decide to continue or carry on.

Generally, I'll know after having read the question whether I can solve it, or whether I need to guess and move on.

Here's a good thread on the topic:
https://www.beatthegmat.com/guessing-3-4 ... tml#315766