You cannot combine string and numeric arrays in a numeric array.
You must use a cell array:
date_01 = '09/01/2015 00:30:00';
press = 5.215;
prm = {date_01 press}
prm =
1×2 cell array
{'09/01/2015 00:30:00'} {[5.2150e+000]}
This should work for your arrays as it did for these two scalars.
You can also combine them in a table.
