Hi,
If you want to use Azure Function and consumption plan which is least expensive, then, bellow is a nice article that describe the behavior of cold start of azure function:
https://mikhail.io/serverless/coldstarts/azure/
If you know that you will have a lot of requests then you can use Premium/Dedicated plans and have the option to pre-warm the function:
https://learn.microsoft.com/en-us/azure/azure-functions/functions-scale
Hope this helps!