Payment is required at the time of the tax sale or a few days later. Some auctions require advance deposits or proof of funds. If you do not pay, you may be banned from future tax sales. A few weeks after the tax sale you should receive a tax sale certificate.
The tax debtor and other interested parties (such as mortgagees or lienholders) have three years (18 months for blighted/abandoned properties) to redeem the tax sale. The redemption period starts on the day the tax sale certificate is recorded in the conveyance records.