From experience working with a number of RSLs that is at the top end of number of the number of visits across the sector. There is no stipulated level of calls or visits, you would just have to show you took “reasonable steps” to try and gain entry to carry out the service.
As an average I would say there would be two contractor attempts and then two further letters from the landlord. Interspersed in the process would be phone calls and visits from landlord staff that should all be recorded.
I am sure others will be able to give you specifics of their processes as opposed to my overview.
Hope that helps