Three to six months ahead is a comfortable general timeline, giving enough room to research and choose between a cruise, land tour, or combination, secure good ship and cabin availability, and sort visa requirements without last-minute pressure.
Why the visa timing matters
Egypt's e-visa is valid for up to 3 months from issue (per the official government portal), so applying too far in advance can actually work against you — it's worth timing the application closer to departure within that window rather than immediately after booking. See Do You Need a Visa to Visit Egypt? for the full comparison of visa options.
Winter high-season travel (December through February) benefits from planning even earlier for the ship and flights, since the best cabin categories sell out first for exactly the months when the weather is most comfortable — shorter-notice trips, six to eight weeks out, are possible but come with more limited choice.