What is a reasonable reimbursement time for conference travel from a department?
Just my two cents.
Departments pay after they receive the necessary invoice from the student. So, they cannot pay hotels before you return from the conference.
In my department, buying the air tickets is not enough. I also have to provide the boarding passes that I actually used the tickets. That means you can only get the air tickets money AFTER returning from the conference. This makes partly sense, because if you got sick and cancelled the trip they would not have given any money to you in advance, so you would not have to return them back.
In many conferences (for CS), you get the registration invoice at the desk and not when you pay online. Again, this invoice is needed for getting back the money you paid, since most institutions cannot provide funding without invoices.
Logistically you might make a reservation in 2014 and the trip is going to be in 2015. Institutions cannot pay money in 2014 for an invoice issued on 2015. This might also occur for smaller logistic periods (every 3 or 6 months) as well, depending on the country's tax laws.
Bottom line. You should start counting time AFTER coming back from the conference. Expecting to be paid in advance without providing the proper invoices is simply not possible. After that, it depends on each department's bureaucracy on how soon you will get the money. And believe me six weeks does not seem that far fetched too.
It is standard for departments to wait until after travel to process reimbursements. In fact, many require boarding passes or other proof that travel occurred that are impossible to provide before travel finishes. Some departments will reimburse before but this is (in my experience) the exception not he rule.
Reimbursements after the fact will vary based on the specific bureacratic rules for approval, the people doing the processing, and the backlog that the administrators are facing. I've had travel reimbursements processed in three days and in three months at the same institution.
Two general pieces of advice:
Remember that administrators are humans who understand that carrying the costs for travel can be difficult — especially for graduate students who are more likely to live paycheck-to-paycheck and carry these kinds of bills on their credit cards than faculty. I've made my situation clear to the folks doing the processing and had my reimbursements bumped to the head of the queue.
In the future, keep in mind that administrative assistants can often purchase plane tickets, conference registrations, and hotels on university credit cards. If cashflow is tight, look into doing this ahead of time to keep this situation from occuring.