convert 16 digit timestamp to excel date time

Your solution has 14 digits. What would the example you presented end up being
1296308149533530
IF we're looking in order, then 12 is the month and 96 is the day!

What I'm trying to get at here is..
How does 1296308149533530 convert to 2-1-2021 (and what happened to hh:mm:ss)?

You've got to give us some "meaning" to that time stamp. It does not seem to be a UTC or TAI time (usually some kind of "seconds/milliseconds/similar" since 1/1/1970). Feb 1 2021 would be something on the order of 1.612E9 seconds since 1/1/1970.

A 15 or so digit integer, I would guess, would be micro/nano seconds since some reference date/time. As a wild guess, I note that that many microseconds since Jan 1 1980 is jan 28 2021. Beyond that, I haven't got much to offer.

With
1296308149533530

with
2-January-2021 = 44198
or
1-Feb-2021 = 44228

could not find any clue that helps

I played with this a little bit but hard to do with a single data point. Since clfletcher is from USA, I assume we are talking about Feb 1, 2021.
To get the number into "Date" range, assuming a simple conversion, it has be be in microseconds
=INT(1206308119533530/(24*60*60*1,000,000)) gives 13961 or 22 Mar 1938.
To normalize that to Feb 1, 2021, one would have to add 30267 (or 12 Nov 1982)
Doesn't really make sense unless that's based on some software start date. Again, a second data point would help.