How do I convert relative Gregorian days since 1935-01-01 to calendar datetime (days with hours,mins,sec)?

I have a netcdf dataset that reports timestamps as decimal values where each represents the "Gregorian" days since 1935-01-01 (1935, January 1), 00:00:00 UTC. I'd like to convert those decimal values to datetime values that we're use to: Year/Month/Day Hours:Minutes:Seconds.

I've never asked myself "how do we compute the calendar days to tell which day of the week it is?" or "what is the anchor date that we use to compute calendar date?" so the subject of "Gregorian" vs. "Julien" calendar is new to me. What does Matlab use?

Attached is the netcdf file I'm working with. You can get the datastructure with the dates using the matlab function call:

ncread('NorthPlatte_2.nc', 'date_time');

Answer 1

[Guillaume]

Probably,

dt = datetime(yourtimestamps*24*3600, 'ConvertFrom', 'epochtime', 'Epoch', '1935-01-01')

[Peter Perkins]

Or perhaps

datetime(1935,1,1,'Format','dd-MMM-yyyy HH:mm:ss') + days(yourtimestamps)

It's almost certain that since the epoch in your file is described as 1935-01-01 (1935, January 1), 00:00:00 UTC, that you don't need to deal with Daylight Saving Time, but in general, yoiu;d want

datetime(1935,1,1,'Format','dd-MMM-yyyy HH:mm:ss') + caldays(yourtimestamps)

if DST were an issue. In any case, using caldays never hurts.