Battery Service Message

Run the Apple Diagnostics to see if any hardware issues are detected. Unless the diagnostics report an issue with the Battery you do not need to replace the battery until the battery no longer performs to your expectations. Unfortunately Apple changed the reporting of the Battery Condition beginning with Catalina so now users get a very generic "Service Recommended" condition once the battery Full Charge Capacity drops below 80% of the original Design Capacity. For some people this capacity is not enough while others may be Ok with the capacity dropping to 70% or more especially if the laptop is always plugged into a charger.

If the diagnostics show a battery failure, then the battery should definitely be replaced. Otherwise only replace the battery when it no longer performs to your expectations or needs.

You need to speak with an Apple tech to find out estimate repair times for your region.

Yes.

Quote:

You'll see one of the following status indicators:

• Normal: The battery is functioning normally. 
• Service Recommended: The battery's ability to hold charge is less than when it was new or it isn't functioning normally. You can safely continue to use your Mac but you should take it to an Apple Store or Apple-authorized service provider to get your battery evaluated.

https://support.apple.com/en-us/HT204054

Battery Service:https://support.apple.com/mac/repair/service