Whilst working on my continental map, I wondered how long the trade routes I had
drawn in would take to sail.

Google came up with this nice resource:

From it I distilled the following for ancient ships:

Sailing in favorable winds, open ocean: 4-6 knots, ~180 to 270 km per day.
Sailing in favorable winds, near coast/islands: 3-4knots, ~130 to 180 km per day.
Sailing in unfavourable winds: 2-2.5 knots, ~90-110 km per day.

For a fleet, given that there will be slow transport ships and just keeping the fleet together will halve these speeds.
A tririme under oars can get up to 8kts, but not for a long journey.

There is a lot of room for differences based on ship type and weather conditions.