First try this: Go to your wifi settings, and tap your wifi network that you're on. Tap forget. Turn off the tablet
unplug your modem and router and leave them unplugged for 30 seconds.
Plug in your modem and let it connect - about a minute, or until all the indicator light settle down
Plug in your Router, and let it connect - about a minute.
Turn on your tablet. see if you can connect to your network.
Try to change your timezone back to how it was.
If that doesn't work....
Go to Settings > Accounts
Delete your Gmail account. (don't worry, you won't lose any data that's on your device).
Reboot
Tap on a Google app (Gmail, YouTube, PlayStore, etc). You'll get a box popping up asking if you want to add an account or use and existing one. Tap "existing" and enter your information. That SHOULD get you back in.