Using Channels DVR there is no way to change the guide update times, except for custom channels that use an XMLTV guide source.
You could create a user defined script in Synology Task Manager that runs Mondays at 5pm Eastern time to update the guide data using the command
curl -XPUT "http://127.0.0.1:8089/dvr/guide?force=true"
where 127.0.0.1:8089 is the ip address and port of your Channels DVR server
This does the same thing as
Settings > Guide Database > Maintenance
Re-Download Entire Guide
Fair warning to anyone doing this. Excessive guide downloads could lead to your subscription being cancelled.