It really depends!
We’ve had many adverts made and let on the same day before.
Other times, if a landlord is advertising a few months in advance of the property being available, it can take weeks to go from viewing to moving in.
The timeline generally is faster in large cities and slower in more rural areas. Tenants and landlords should discuss their ideal timelines at the earliest possible chance - such as while messaging or at the viewing.
The part of the process that takes the most time is probably referencing, which moves as quickly as the people involved want it to. If the tenant is slow to provide references, info, etc. then it can take a few days.