Application timeline for 1L summer jobs

Incoming 1L here with an idiotic question. I could probably find the answer to this online somewhere, but I figured it'd be faster to hear what reddit has to say.

My understanding is that getting a summer associate position at a big law firm in the summer after 1L is very hard, much harder than getting the same type of position in the summer after 2L (even though that's also hard, of course, depending on the school one goes to and one's grades). But I take it it's really important to have something law-related on one's resume for the 1L summer. And I gather various types of legal internship and externship (don't know what the difference is between these two things, but that's not what this post is about) are examples of valuable things to do.

My question is about the application timeline. When do 1Ls typically apply to jobs/internships/externships for 1L? I read somewhere that applications for certain jobs that law students might be interested in for their 1L summer open in December 1. That seems odd to me because that's before a 1L would have any law school grades recorded. What would employers look at then? Just whatever's on the resume from before law school as well as whatever law school one is attending?

Or is it more of a situation in which, though the applications for certain jobs/internships/externships may open before any of a law student's grades have been determined or exams have been taken, realistically no one applies, or no application is considered, until some grades have been received?

Maybe it depends on what exactly one is applying for? I have heard that some employers who hire law students for 1L summer positions don't care much about grades, whereas others care quite a bit.

Anyway, any clarification regarding the timeline for applications for 1L summer jobs would be much appreciated.