Calling DateDiff directly in vba6.dll or msvbvm60.dll

Hi

I'm developing a C# app which needs to be multi-targetted at NetCore3.1 and NetStandard2.0. I need to call the DateDiff function.

I'm struggling with the Microsoft.VisualBasic namespace and NetStandard versions since the DateAndTime class doesn't seem to be present in NetStandard2.0 although strangely it is there in NetCore3.1.

So I am wondering if it would be easier just to call directly into the vb6/vba libs themselves. Colleagues have found pure C# code which seeks to replicate the DateDiff function has slight discrepancies with what vb6 has returned and we are running the 2 apps (old vb6 version and new c# version) side by side.

Does anyone know if that is going to be possible?

I'have had a look at dependency walker and can see rtcDateDiff function in msvbvm60.dll and it's entry point, but I can't work out if it is exposed in a friendly fashion and if so, how to call it. I guess it must be, since it is surfaced to vb6/vba. Further, I'm not sure how you would pass dates to the functions in either of these dlls.

Any guidance or links/sample code would be welcome.

Many thx in advance.

s