Hi,
On Method CRM for Quickbooks, there is no default way to block off certain dates for holidays in the activity calendar. This goes for both desktop and online. You said you could do this in the desktop version, was this through customization?
You can achieve this type of function through customization. You could create a date check function, where a table with the dates you want blocked is created and used to check those dates a newly created activity. Additional customization may need to be done to account for a series, as these activities will be created without going through the date check.
- Adam