Cover Driver will start you at a higher wage but is technically a part time position (though you'll work full time hours).
Speak with your steward. If they are going to be hiring a lot of 22.4s I would start as a cover to get red circled at the higher rate and then go 22.4 as soon as possible. There is no wait time and also you don't have to qualify again. They just make you a 22.4.
Cover driver starts at 70% of top rate and goes to 75% after 6 months.
22.4 starts at $20.50