Is the live version in use by other users while you are making changes to the dev version?  If so, then you and your users cannot make changes to the same tables in the dev and live versions.  If that's impossible to do, then my advice is don't go live until you finish all your developmental work.  After you go live, if you want to make changes again, put the live server offline, make changes, then put it back online when you finish.

Are you making changes to existing Tables (or other objects)?

Yes, that makes perfect sense. The usual approach is to have separate Development and Live SQL Server databases, just like you have separate Access front ends now.

You can build and test the SQL Server tables on your computer first. When you are ready, move the database structure to the live SQL Server using a database backup/restore or scripts generated from SQL Server Management Studio. For the initial conversion, you can also use the SQL Server Import and Export Wizard to move the Access data into SQL Server.

The important part is that, once users are working in the live database, it becomes the authoritative copy of the data. You don't want people entering or editing the same records independently in both Development and Live, because merging those changes afterward gets messy quickly.

For future changes, make and test the table changes in Development first, then apply the same changes to Live during a planned deployment. You normally do not have to take the entire SQL Server offline. You may need to briefly stop users from using the affected Access forms while you make a structural change, especially if you are adding required fields, changing data types, or otherwise altering a table they have open.

Also keep your Access front end separate from the data. Your Development Access file should link to your Development SQL database, and the Live front end should link to the Live SQL database. When you deploy a new front end, distribute a new copy to the users rather than having everyone open one shared front-end file on the network.

Thank you everyone for your input.