Never understood the need for meditation retreats. The only purpose of gathering would be to meet and converse with other people. Not to sit and listen to them breathe.
Formal Buddhist training - such as to be a teacher within the Kadampa tradition - can be done once a week over a course of years. Other traditions training requires full-time reading training over years.
I wouldn’t recommend someone try to master an instrument in 7 - 14 days as learning takes time for integration and people progress at different rates. So I’m skeptical of why anyone would suggest that for attempting to master the mind.