The actual Three Peaks Challenge involves climbing the highest peak in each of England, Scotland and Wales in 24 hours. The time taken must include the drive times between Ben Nevis, Scafell Pike and Snowdon.
If this isn’t for you then there’s the option of a less intense approach, climb a peak a day, do it as a relay or however you like. The only stipulation is that all three Peaks must be climbed but not necessarily by the same people or in a set time. It’s up to you.
Most people choose to start in Scotland and work back down but again this is a choice.