As Panagiotis Kanavos pointed out earlier (in the staging phase) - the 'hoursDiff' value is the same between the two runtimes (it can be proved by printing the entire double using the 'N20' toString parameter).

Therfore, the issue must be related to differences in the DateTime object.

After further investigation of the NET DateTime documenation I have found that there's been a change in the rounding behavior inside the DateTime.AddHours method which I beilive is the source of the issue.

Source - https://learn.microsoft.com/en-us/dotnet/api/system.datetime.addhours?view=net-7.0