I said 30 seconds, but let me qualify it. This is for d20. I get away with 30 seconds for 2 reasons:
1) CMG SRD on my laptop.
2) Divide and conquer: "Eric, look up feat X. Joe, I want you to check if feat y or skill z grants a synergy bonus".
For 1e and B/X I generally just know it, or someone else at the table does.