Is there a time that IRS is not accepting E-filing for tax returns?

Yes, IRS has stopped receiving e-filing for tax period 2019 starting November 21st, 2020 for individuals and it will stop receiving business tax return on December 26, 2020.

Individual Returns

The individual shutdown for tax year 2019 begins on Saturday, November 21, 2020. Submission transmission ends at 11:55 p.m. EST; acknowledgment retrieval from IRS ends at 11:59 p.m. EST. 

This shutdown will prevent e-filing of individual returns.
Any acknowledgements not retrieved by 11:59 p.m. on November 21st cannot be accessed until MeF opens for production in January 2021.
At that time the current and two prior years can be e-filed. 

Note: The IRS has extended filing deadlines for some taxpayers affected by natural disasters (wildfires) to 12/15/2020, however, the e-file system will not be available during the shutdown to allow for e-filing of those returns. Any individual returns needing to be filed between November 21, 2020 and when the IRS opens in January 2021 will need to be paper-filed. 

Business Returns

The business shutdown for tax year 2019 begins on Saturday, December 26, 2020. Submission transmissions end at 11:59 a.m. EST; acknowledgment retrieval from IRS ends at 11:59 p.m. EST. 

This shutdown will prevent e-filing of business returns.
Any acknowledgements not retrieved by 11:59 p.m. on December 26th cannot be accessed until MeF opens for production in January 2021.
At that time the current and two prior years can be e-filed. 

States

States can continue to use all the service requests necessary to retrieve and process state submissions until shutdown activities shown above. MeF recommends that states adjust their processing schedule in order to retrieve submissions in time to validate returns and submit acknowledgements.

Some states, such as California, still allow for e-filing of state-only (a.k.a direct) individual returns even when the IRS is shutdown. 

More MeF service information may be available at the IRS MeF Status Page.