How long did it take the British armadas to get to the Americas just before the start of the Revolutionary war

The British never used the Armada, that's a Spanish term for fleet.

AS in the "Spanish Armada" was sunk off the coast of Great Britain by a terrific storm.

British Forces in all the Colonies were regularly roated or reinforced there was no specific rush to the Americas with a special force of Navy ships.

An Atlantic crossing could take anywhere between 2 weeks to 50 days, depending on the direction, and the time of year for a sailing vessel in the 18th century.

A fleet made up of dispatch vessels, frigates and 1st, 2nd, and other higher rated men of war would not be making a very fast passage. The larger ships were more powerful, ( larger hull, better sea keeping abilty, stronger press of sail), but most heavy English men of war were full in the lines, blunt bowed, and broad of beam. I would think 8 to 10 knots under the best conditions.

Depending on the directon of the wind and prevailing seas

the time to cover the distance from Europe to America could vary. Even so, the transport and supply ships may be the slowest sailors in a convoy and accordingly would set the pace for the entire group.

In the days of the Black Ball packet ship, that sailed on the first and the 15th of each month to and from Europe from the states, a passage beating into the wind, having to tack, or wear if the ship was loose in stays...this could add a week or more to a crossing.

Figure on 2 to 3 weeks. But I have read of passages taking 57 days or longer. And they would not be in fighting trim on arrival. Water, wood, and stores would all be pretty low by then.

A rapid crossing was about three weeks if all went well. More common was 5 weeks to three months. And once arriving the ships were rarely ready to go right into action. They needed to dock to make repairs, resupply, replace sick or dead crew, etc.

I believe the trip back then took several weeks.