The stimulus funds are dispersed by the IRS on the schedule devised by the US Treasury.
https://www.irs.gov/coronavirus/economic-impact-payments
To help everyone check on the status of their payments, the IRS is building a second new tool expected to be available for use by April 17. Get My Payment will provide people with the status of their payment, including the date their payment is scheduled to be deposited into their bank account or mailed to them.
An additional feature on Get My Payment will allow eligible people a chance to provide their bank account information so they can receive their payment more quickly rather than waiting for a paper check. This feature will be unavailable if the Economic Impact Payment has already been scheduled for delivery.