Question

I met/'ve met them at 10 a.m​

Answer 1

Действие началось в определенное время и все ещё продолжается, значит предложение является Present Perfect. Следовательно, оно будет звучать так:

I've met them at 10 a.m

Answer 2

Both "I met them at 10 a.m." and "I've met them at 10 a.m." are correct, but they have slightly different meanings.

"I met them at 10 a.m." implies that you met someone specifically at 10 a.m. in the past. It is a simple past tense sentence indicating a completed action at a specific time in the past.

"I've met them at 10 a.m." uses the present perfect tense. It suggests that you have had the experience of meeting them at 10 a.m. at some point in the past, and the exact time of the meeting is not specified. Present perfect tense is often used when the exact time of the action is not important or when the action has relevance to the present moment.

Both sentences are grammatically correct, but the choice between them depends on the context and the intended meaning you want to convey.