CDC hasn't made the formal recommendation yet for 8-month booster for all - it's "being reported" that this will be the case, so likely will be the case "soon". I expect that once the formal recommendation is made, then the time-line will be firmed-up (they're saying 8-months, since it's a 6-12 month "window" for the booster after full vaccination). For myself, my 2nd Pfizer was on 4/12, so my full vaccination date was 4/26 - which would place my 8-month Booster at/around xmas, with the "window" being from October - April. Royal will evaluate and make changes down the line, but I wouldn't expect anything right-away.
If I were to place a bet, it would likely be that they require you be "fully vaccinated" within the past 12 months AND/OR have a booster logged within the past 12 months (since, this will likely be something akin to an annual Flu-shot as variants die/emerge/compete - like the Flu variants).