Q: how to revert to lion using time machine

Do you have a full system backup of Lion that has not been corrupted by backups from later versions of OS X? In other words it must be a clean backup. Otherwise, you would need to use a Lion installer to do such a reversion because you would also need to erase the drive (in either case.) If you don't have a Lion installer then:

You can purchase Lion at the Online Apple Store. The cost is $19.99 (as it was before) plus tax.  It's a download. You will get an email containing a redemption code that you then use at the Mac App Store to download Lion. Save a copy of that installer to your Downloads folder because the installer deletes itself at the end of the installation.

Or you can post what problems you are having with Yosemite to see if they can't be solved. You can also search the forums for solutions already posted. Most reported issues have been asked and answered many times.

Sorry, but I haven't a fix for that. Here is what I do have:

Five quick fixes for Wi-Fi troubles in OS X

Recommended settings for Wi-Fi routers and access points

Wherever possible use Ethernet if you can. If you have a wireless mouse and BlueTooth keyboard, then turn off the keyboard to see if it is interfering with the Wi-Fi. Or use a wired mouse to test. If you have a microwave oven nearby then it can cause serious problems with Wi-Fi when it is running.

Wi-Fi Problems in OS X Yosemite (2)

Wi-Fi Problems in OS X Yosemite (3)

WiFi Potential Temporary fix - Yosemite

Also try turning off Bluetooth.

WIFI AND BLUETOOTH FINALLY SOLVED, NO REALLY - YOSEMITE 10.10