If you haven't already done so, I recommend reading through the DODMERB forum to glean insight.
In general, DODMERB's role is to Q or DQ per existing accession guidelines, and be the central clearinghouse and collator for additional info requested.
The SA grants or does not grant the waiver.
Length of time will vary with the complexity of the case and the case review docket.
Not helpful, I know, to your specific question. Internal to the process, "they" will be working hard to clear the waiver actions, make decisions and get on with filling out the class.