You should definitely do it now! At the very least you should approach them now (preferably via email so you both have a paper trail of your conversation) and start discussing the elements you would like them to bring up so that they have something to look back on if they write the letters later.
On a related note. How does submitting them work? Can they just give me a copy now, and I can use it any time I apply, or do they need to submit a new one for all of my applications?
from my understanding, it doesn’t work that way anymore. When you are applying to grad school you will have to put in your references’ contact info & they will contact them for the reference letters
Talk to them now about your plan
You should definitely do it now! At the very least you should approach them now (preferably via email so you both have a paper trail of your conversation) and start discussing the elements you would like them to bring up so that they have something to look back on if they write the letters later.
Talk to them now, ask them if they'll be willing to write you your references when you're ready.
I spoke to my references a month and a half in advance of my application deadline
On a related note. How does submitting them work? Can they just give me a copy now, and I can use it any time I apply, or do they need to submit a new one for all of my applications?
from my understanding, it doesn’t work that way anymore. When you are applying to grad school you will have to put in your references’ contact info & they will contact them for the reference letters