There is a java action in the Community Commons module for converting Unix timestamps(ms) into DateTime. https://docs.mendix.com/appstore/modules/community-commons-function-library#4-2-datetime
Depends on the format of your float but if it was the Unix timestamp in seconds then could times by 1000 to get milliseconds, convert to integer/long and pass into the LongToDateTime java action.
Example values as shown in the SQL database all result in 1/1/1970 when using the epochToDateTime function: 41943.5662240625
When debugging with the following values in the SQL database:
41943.5662240625 and 42395.4232387731
I get the following values in the variables:
the epochToDateTime expects an Integer as input, however the values in the SQL database look like Decimals.
When I change the input parameter to a Decimal, then this epochToDateTime function generates an error in StudioPro.
How are you exporting the data from your SQL database?
If this is using Transact-SQL, you would be better running the value through CONVERT on the SQL Server.
SELECT CONVERT(datetime, 40486.6908449074)