There's no needing to wait unless you elected an actual refund. Issuing an ecredit is a misnomer. There's nothing issued. The unused eticket simply shows up under "ecredits." Ecredits aren't really a thing but a heading.

Simply select ecredit from my wallet, or if doesn't show enter the eticket number. Can rebook right away after canceling reservation. I do this when modify doesn't work on reservation. Cancel it, search for new flights and enter the eticket number for payment as an "ecredit "