MATLAB: Read in dates (for timestamp) from file names

datenum

I am trying to read in data and the measurement timestamps do not include the dates. The filenames include the date/time when the file was started. How can save the date from the filename to use it in the timestamps for each measurement?
I was previously doing this: 
filepath = 'HR3_181920/PH/';
filelist = dir(strcat(filepath,'*.txt'));
file_timestamps =cell2mat({filelist.datenum});
But this doesn't work because it is taking the date from the structure for the datenum value which I think is actually the time when the file ends (not the beginning). I have attached a file of the resulting structure which includes the names of the files I am trying to work with.
These are the 'file_timestamps' that I currently get when I run those line. Notice they match the date column but not the information in the name of the file. 
        2018           7          18          12          49          50
        2018           7          18          12          54          48
        2018           7          18          17           3          58
        2018           7          19           0           0           2
        2018           7          19          11          50          12
        2018           7          19          11          54          18
        2018           7          19          18           5           4
        2018           7          19          18          25          20
        2018           7          19          19          50          54
        2018           7          19          20          26          12
        2018           7          19          20          26          36
        2018           7          19          20          27          20
        2018           7          19          20          28           6
        2018           7          19          20          28          54
        2018           7          19          20          29          58
        2018           7          19          20          32          28

Best Answer

Just parse the filename itself...
fmt='yyyyMMMdd_HH-mm-ss';
tstr=cellstr(strvcat(d.name));
file_timestamps=cellfun(@(x) datetime(x(1:18),'InputFormat',fmt),tstr);
or just do each inside the loop and can do without the conversion to cellstr array and cellfun to just parse each substring.
ERRATUM: I had a t test array; thought better variable name wise but didn't fixup the second reference to match...
...
file_timestamp=datetime(d(i).name(1:18),'InputFormat',fmt);
...
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