Hi, so I just got my assignment on Ao3, but the Dear Creator letter's here on Dreamwidth and it says I don't have access to said letter even after I made this account (solely for the purpose of reading the letter). I have no idea how this site works: is there a period of time I need to wait? Is there someone else who can read the letter and then send me the text of it via something else? If someone can help, I'd be much obliged.

It's hard to be totally sure, but chances are they aren't done writing their letter and are keeping the post locked so people can't read it until they do. They might have signed up last minute or just been too busy to finish it yet. I'd suggest checking back over the next few days to see if they've finished and unlocked it, and if it doesn't get unlocked maybe see if the mods mind ferrying a message to your recipient anonymously asking when it'll be available. Chances are now assignments are out they'll probably be trying to get it completed for you a.s.a.p.

Ah okay thank you!!

What the above person said. It's probably not finished yet. If they don't get it posted in a few days, drop me a note and I'll e-mail them.