You'll be able to submit orders outside of Regular Market Hours (Extended Market Hours). The Extended Market Hours are Pre-Market Hours and Post-Market Hours, during which you may submit orders for US stocks.
Orders submitted for execution during Extended Market Hours can only be Limit Orders in financial instruments, which are whole shares. You may opt-in to trade during Extended Market Hours via the Revolut app. The Pre-Market Hours are 4:00am EST to 9:30am EST time. Orders will begin to queue for Pre-Market Hours starting after the close of Post-Market Hours on the previous trading day, and will be eligible for execution (along with newly placed orders) during Pre-Market Hours.
Any unexecuted or partially filled orders during Pre-Market Hours will automatically roll over into Regular Market Hours and, if still not fully executed, into Post-Market Hours. The Post-Market Hours are 4:00pm EST to 8:00pm EST time. Any unexecuted or partially filled orders during Regular Market Hours will automatically roll over into Post-Market Hours.