Florida Notice to Vacate Letter

[Ethan Brown]

A tenant (not mine) reached out and let me know the house they are in is being sold. They have a notice to vacate by July 31. 

The listing agent who works for the firm who has the property management arm scheduled showings without permission of the tenant. The tenant was polite and let the realtor know she wasn’t able to let anybody in during the stated times.

Subsequently, the tenant received a notice to vacate by July 15. 
If the tenant has the 31 date on paper, can the property management company legally change the date if the tenant did not break the lease agreement?