Antivirus

Why do you want it off, It provides some good protection for a lot nastiness on the web.
Roaming the web without virus protection is an invitation to disaster.
Most 3rd party antivirus will turn it off replacing it with its own version
I run Norton Antivirus and Malwarebytes as backup.

huffman said:

I don't know how long it stays off. Is there anything I am missing by just click the icon to turn it off?

Windows automatically enables it, if it detects no realtime antivirus protection.

You can try to disable Virus and Spyware protection messages/monitoring.

Turn On or Off Security and Maintenance Messages in Windows 10

Arvid said:

You can turn-off Windows Defender if you want then have only your own Anti-Virus(E.g. McAfee) to run. But maybe don't. Although I don't bother with Windows Defender, I'm sure it is useful in some cases. Instead of turning it off, it'd be best to run both. In that case, if one Anti-Virus fails then you have an extra as back-up.

Either not possible or not recommended. Windows Defender usually disables itself when it notices another AV program installed.
If Windows Defender doesn't disable itself you have the problem of 2 AV programs installed (if they're both running real-time) which can cause lots of issues and may not protect a system as sufficient as a single AV program can.

There are tons of different security vendors whose products are very good. Microsoft's Windows Defender has since some feature updates been significantly improved, so much that it has become a good competition for well known security vendors (such as Avast, AVG, Norton, McAfee and Kaspersky, but not limited to them), that is if it hasn't already surpassed them (competition wise).