How to convert all datenum data to datetime using loop

Hello guys, i am new to Matlab. Right now i have lots of datetime data of same day but in different stations. some stations have recorded 5 sample in one second and others 8 sample in one second. So my questions here, can i use loop to convert all the datenum data in one single loop. Cause i dont want to waste my time convert one by one. And if it can, may you guys help me with the instruction on how to do it. your help very much appreciated. Thank u.

Sample of data

HJO_LHN_t, 
GJM_BlE_t, 
GJM_BlN_t, 
GJM_BlZ_t, 
GJM_LHE_t,
GJM_LHN_t,
GJM_LHZ_t, 
GJM_LlE_t, 
GJM_LlN_t, 
GJM_LlZ_t, 
HJO_BHE_t, 
HJO_BHN_t, 
HJO_BHZ_t, 
HJO_BlE_t, 
HJO_BlN_t, 
HJO_LHE_t, 
HJO_BlZ_t, 
HJO_LHZ_t, 
HJO_LlE_t, 
HJO_LlN_t, 
HJO_LlZ_t, 
HRO_BHE_t, 
HRO_BHN_t, 
HRO_BHZ_t

and others... Some of the data have 1,727,980 row and some have 86,399 row.

[Walter Roberson]

Those do not appear to be datenum data? Those might be variable names, or file names?

[Amirul Azman]

What i mean is as example is like GJM_BHE_t has 1,727,980 set of datenum. I already converted it but the thing is i have lot of this type of data, so it will take lot of my time if im trying converting it one by one.

here an example of GJM_BHE_t :

[Walter Roberson]

How are you creating or reading in all of those different arrays such as GJM_BHE_t ?

[Amirul Azman]

that one i extracted one by one from the data i got from NIED japan. it is seismic data

[Stephen23]

"that one i extracted one by one ..."

Sounds painfully inefficient, as is putting meta-data into variable names, which is really like a shot in your knee before running a race...

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

[dpb]

"...from the data i got from NIED japan"

OK, let's start there. In what form are these data initially? Importing them efficiently is the first step but to help we have to know something about what it is you're actually using as the data source.