The IRS says historcally about 9 out of 10 tax returns are processed within 21 days from when they are accepted by the IRS. If you filed before Jan. 28, yours may not have been actually pulled into the IRS system before that date. If you had EIC or additional child tax credit, your refund would be delayed until near the end of February.
See this IRS Q&A article: https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions