Sorry, I have no usefull idea for this at the moment.
Edit: The SLA topic is a very complex topic and the provided information are not enough.
Please also note that the little time we can provide to the community, might not be enough to help you good enough in this case. I’m sorry.
Normally the answer would be no here (ignoring your possible use case).
Let’s take IT system houses as example, because this might be an easy example.
You have service contracts with your customers. In this contracts, you guruantee your customer that your initial reaction on his tickets / issues will be 1 hour (as example). In this case, it wouldn’t make any sense at all that if the customer adds another article (for whatever reason) to reset the time counter, to 60 minutes, because you didn’t react yet!
Update time forces the agent to communicate regulary with the customer in defined time span, over and over again. This doesn’t always make sense, but if it does, you don’t want to choose a too small value, because you’ll be busy with answerin instead with working on the issue directly.
Also, you can’t enforce SLA on your customer (if that’s the second thought), where would we go ? … 
Please don’t get me wrong, I’m understanding your approach, but with current possibilities it’s not possible to achieve this.
From this point, you have three options:
- create a feature request and hope the feature to come somewhen in the future™
- a custom development for an addon that enhances your Zammad instance with the wanted functionality
- you custom code your own addon (see: Examples of zpm files? - #3 by thorsteneckel )