For exapmle, you get a new girlfriend, and your friends or parents say:"come on, bring her here, and let's have a see."(带出来让我们见一见啊。) “什么时候也让我们见一见啊？” doesn't really mean to ask you the time to see or meet. It means "how about letting us have a see someday?". You could just answer:"好啊。/没问题。" rather than a real time. I'm not sure whether I am understood.

verb + 一 + verb or verb + 一下 means an action happens very soon. for example, 让我想一想。or 让我想一下。 let me think. or let me see. it means let me think a little while. I need think but i just need a second for thinking. another example, 我能看一看(下)你的新手表吗？ can I see your new watch? it means I want to see your new watch but I just see it a little while---one second. but this usage is just for those verbs whose actions can be last. for example, think, see, listen, teach, etc, for these verbs: come, go, die, etc you cant use them like this: verb+一+verb or verb + 一下 normally, in any normal conversation, we always say like this: 让我想一想 我们一起去逛一逛街(逛街：go shopping) etc

what time let us meet? 一 between verbs means short action

It must be in a context to get to know what it really means. Both answers below are correct.