Sure, it’s easy. 
It’s the same principle as using a virtual timer for a light switch when you still want to be able to use the light switch without a timer under other conditions.
Instead of setting up your Alexa routine to trigger when the actual sensor opens, instead, create a virtual sensor in SmartThings. And use the virtual sensor to trigger the Amazon routine.
Use a DTH which is both a sensor and a switch so you can turn it on and off with the official smart lights feature or any other automation you want to use. (More on this bit later)
Now create a rule so that when the actual sensor opens and it is between the specific hours when you want the announcement, turn on the “switch” which is the virtual sensor.
That way echo will only speak your notification at the times when you have turned on the virtual sensor. (Remember to turn it off again so it will be ready for next time.)
More details about all of this, including the DTH you can use, in the following FAQ (this is a clickable link)