It is certainly possible for you to be able to receive your refund in less than 21 days, but there is no guarantee. The IRS processes your returns and, once they are accepted, will process your refund. Most of the time, the IRS can issue your your refund in 21 or less.
Please note, some tax situations can make the process take longer. Some of the things that can slow the process are if you qualified for Earned Income Credit or Child Tax Credit, or if you efiled your returns without entering a state-issued ID.
You can track your refund using the Where's My Refund tool on the IRS website (given below).
https://www.irs.gov/refunds