Hi,
I am developer with more than 4 years of experience.
As you probably know the amazon echo skill functions are self hosted by users and can be additional cost involved if they are used on many devices.
What i am proposing here is to use AWS Lambda functions and host it there as ( free tier would suffice for Your personal use (1 mil lambda seconds))
Code behaviour:
Voice command invokes the skill code which then calculates the result on AWS Lambda and returns response time for you.
Yours sincerely,
Ivan Klinac