Hi there 
welcome to the forums!
It sounds like you need a function timeout increase. We can definitely bump you up to 26 seconds, but you’ll need to be on the Pro tier for us to make that change - that’s a requirement that applies to everyone who wants a bigger timeout. You can upgrade to Pro easily through the Netlify UI dashboard.
If you don’t want to upgrade your tier you can give this support guide a read this may help you minimize your use of functions so it doesn’t timeout as easily. [Support Guide] Why is my function timing out?