Unfortunately that can't be done. A routine is enabled for every device on your account. You can't disable it for only certain devices. It's either on for everything or off for everything, and nothing in between.
Yes, Alexa routines are very primitive compared to Google Home. Home allows one routine to perform multiple commands at different specified times.
For instance, I have routines that I use for normal work days, that wake me, give me weather, turn on lights, heaters or air conditioning control, start and turn off a coffeemaker, turn off lights, etc. and this is done over various times. With Alexa, I have to do this with many separate routines and if I'm not going to be working like a holiday or vacation, I have to go find all these routines a disable them. It's a pain.
In Home, I just have one routine for work days and I can do everything because you can set the times for everything to occur in each command, so all I have to do is disable one routine.
I have used both of these systems extensively and each have advantages and quirks. Alexa timer functions are better because you can set a timer on a device and hear it on another, but Home is better when it comes to stopping a timer because all you have to say is "Stop". You don't need a wake-up word.
Both systems bug the heck out of me for their incessant and unneeded additional speaking, such as repeating nearly every command you give them. It is quite obvious that when I ask a light bulb to be turned on or off in the room I'm in, I know whether it has happened. Additionally, Alexa often just starts babbling on about things I have absolutely no interest in: "By the way, did you know that I can talk excessively about topics that you don't care about?"
These companies really need a consultant who understands logic.