First of all, if you need a recommendation tomorrow, I'll give you my answer right now: NO.
If you need a letter for the Single Subject Credential Program here, I require at least five days to fill the form out.
Now before you ask me to write a detailed letter for a job or graduate school, I need you to collect some information for me. I expect you to look at these two web sites which list all the things I will need to know about you. The first one is maintained by the Cal Career Center, and the second site belongs to a professor at Harvey Mudd College.
I require at least three weeks to write your letter. Moreover, the three weeks begins after you provide me with the information I have requested above, and not the day you ask me for a letter.
One final thing. Any letter I write will be honest and accurate. If you worked extremely hard or got a good grade (or both), I will certainly say that. But, do not expect me to say only positive things about you and not mention any glaring negative things. If you received a B in my class but you could have earned an A had you actually applied yourself, I will say that. If you came to class only half the time but still managed to pass with a C, I will say that too.