Setting up Time Machine via Linksys AC1900 router to backup to networked hard drive

I want my Time Machine to use the networked hard drive via Linksys AC1900 router as a backup. I can access the networked hard drive through Finder, but can’t seem to get Time Machine to recognize the Hard Drive attached to the router. I have files that are Windows based so I want both Mac and Windows files to be backed up.

I am using Macbook Yosemite 10.10.5

Appreciate any help. Thanks.