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Yourdate_time__c + (minutes/1440)
Explanation:
1440 is the number of minutes in a day
A date-time field in Salesforce is a combination of a date and a time.
The time is represented as a fraction of a day, where 0 represents midnight and 1 represents the end of the day.
For example, 0.5 represents noon, and 0.25 represents 6:00 AM.
So when we add a fraction to a date-time field, we are effectively adding a certain number of days, hours, and minutes to the original value.
https://developer.salesforce.com/forums/?id=9062I000000XsMAQA0