Steps to check the Up/Down status report of firewall in NSM SaaS:
Login to NSM by logging into https://cloud.sonicwall.com. Go to the Firewalls->Inventory->Click on a firewall for which the report is needed. It will switch to the Firewall View.
Click on the Monitor Tab--> Overview-->Up Time Report-->

We can view for this report for Last 12 hours, 24 Hours, 3 days, 5 Days, 7 Days and 30 Days. Also we can go with specific dates or Date Ranges.

NOTE: This report option is available only with NSM version 2.5 for Firewalls running on SonicOS version 7.1.2. After upgrading firewall to 7.1.2, Reconfigure Reporting and Analytics need to be performed in NSM for the firewall in order to configure this report type.
Steps to peform reconfigure reporting and analytics: Reconfigure Reporting and Analytics in NSM