I don't know, I got mine after talking to a realtor and finding a house.. everything was stressful and last-minute for me. I would imagine they aren't good forever since your bank account is static.
Make sure you have at least 4-5 thousand bucks in your account. If you parents/friends gift it to you, you'll need to fill out some gifting letter saying something along the lines of "this money is a gift and not to be paid back, it isn't just for the house" along with two previous month statements from that account.