You probably want the Condition to be Due Date less than or equal to Now plus 1 Hours.
If you want a complete pre-made solution… what you’re seeking is called “Drip Marketing Campaigns”
Maybe one day, an upgraded/simplified Campaigns module will provide the essentials of drip marketing inside Suite…
Marketing automation service providers offer monthly subscription plans which perform Drip Marketing Campaigns. AWeber, Mailchimp, Infusionsoft, Pardot, Inbox25, Constant Contact.
You can buy prebuilt drip email marketing automation modules on SugarOutfitters for running drip email campaigns from SuiteCRM.
MyCRM Drip Email Campaigns module, Process Manager by SierraCRM, and SugarChimp module, with 30 day trials… !
Links provided for convenience… Not affiliated with any of the above companies…
https://www.sugaroutfitters.com/addons/drip-email-campaigns-module
https://www.sugaroutfitters.com/addons/drip-email-campaigns-module
https://www.sugaroutfitters.com/addons/process-manager-enterprise