SSRS (SQL Server Reporting Services) shuts down some services and restarts others after a period of inactivity. By default, this period is 720 minutes (12 hours). Once the services have been shut down, the first attempt to process a report takes much longer to process because these services must be started. This is most noticeable when printing for the first time each morning.
There are two things that can be done to alleviate this issue.
1) The first action is to change the default value for "RecycleTime" within "rsreportserver.config"
Report Server 2012, 2016, and 2019 all have different paths to this file. However, it is generally found under C:\Program Files\Microsoft SQL Reporting Services\SSRS\ReportServer.
"rsreportserver.config" is a critical file. So make a copy of this file before yo begin editing. Use FIND to search for word "recycle". There should be only a single tag match which reads as
2) The above step will partially resolve the issue by at least extending a portion of the restart functions to once every 25 hours. However, another embedded function will still cause a minor delay to running a first report of the day. To address this, I suggest that you reschedule one of your Report Subscriptions to run at a time just prior to the beginning of your business day. Then when business activity calls for a report to be processed, Report Server is fully loaded.