Can I use Time Machine to dump Photos?
Yes, you can use Time Machine to restore iPhoto app and also the iPhoto library before the conversion of Photos app. 


You have to navigate through Time Machine backups and folder via Finder. 
Now go to Applications and restore the iPhoto.app. 
After that navigate to the folder containing your iPhoto library and restore it where you want without overwrite the converted Photos library. 
Exit from Time Machine. 
Open iPhoto and open the iPhoto library.