Can I Use a Second Internal MacBook Pro Drive As My Time Machine Drive?

My Mid 2010 17″ MacBook Pro’s DVD drive can be replaced with a second hard drive or SSD. Can I use this second internal drive as my Time Machine drive?
I find it difficult to attach my external Time Machine drive often enough to make the most use of time machine’s way back feature.
Device: Mac Running Something Older
App: Something Else
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Randall Lee Reetz