Easiest? Perhaps either of two solutions would work for you.
1. Make a batch file that can be launched as an individual process. Schedule it to run at a particular time of day when no one is/should be in the DB. If you want to get really fancy, a VB script can even compute a date suffix for the file name so you can date-tag the file. Have the file check for the existence of the lock file. If no lock, the file is not busy, so just make a complete copy of the BE file.
2. Make a separate Access standalone file that does the file copy and file name manipulation for you. Again, check for the lock file of the target app before deciding to make the file copy. Again, make a complete copy.
In NEITHER case do you EVER want to make a backup of part of the file. I.e. don't even BEGIN to think about making a backup from within the app. Always make the backup from outside of the app. Always make it a monolithic copy operation.
In EITHER case you can launch the backup operation using Windows Task Scheduler set for daily operation at your chosen time. Note that if you use the "Access standalone app" to do the backup, you need to schedule Access to open your app with the /X:macro-name option, and that named macro is the sequence of steps to do the file copy operation. Look up Access command line options to see more of the /X operation. IF you do it this way, ALWAYS end the named macro with an Application.Quit command, because you don't want to leave copies of Access "dangling" after the backup.
IF it happens that you have a 7 x 24 exposure, you have already screwed the pooch. Whether talking Access or ORACLE or some other DB setup, you should ALWAYS have a time set aside to make unobstructed backups. ALWAYS. Forgive the slight implied arrogance, but if your data was important enough to have to be backed up and you CAN'T set time aside for your backup, then you weren't serious about the importance of the data. I learned that from having 28 1/2 years of experience as a U.S. Navy system administrator for a big personnel database. If it is important, be prepared to make accommodations to TREAT it that way.