How to monitor a file whose name has characters between the date?
You can use the FKM plugin, with date codes invoked within the filename pattern.
Suppose you have file that is created daily in which the filename pattern includes the current date. For example, the current date is September 16th, 2021 and a file was created with the name Test_File-y2021-m09-d16.logand you want it detected daily. 
You can use the the following date format code, Test_File-y<today %Y>-m<today %m>-d<today %d>.log, as your Source filename. 
Below is how the FKM view would look like: 
Alternatively, you can do the same for 
Attached is the “Date Format” sampler. Please note this sampler was set up on version GA5.9.0.
Related Articles - Date Generation