Hi @Takahashi Kazuya ( 髙橋 和也 ) we are sorry to hear you're facing this issue. How long are you trying to increase time to timeout in your webapp?
The error `504 Gateway Time-out' usually occurs when your webapp takes more than 230 seconds to return a response.
Currently 230 seconds is a default timeout configured at the Azure App service load balancer. This is a part of the Azure App service architecture and cannot be configured or changed.
If your web app requires background processing, we recommend using Azure WebJobs. The Azure web app can call WebJobs and be notified when background processing is finished. You can choose from multiple methods for using WebJobs, including queues and triggers.
WebJobs is designed for background processing. You can do as much background processing as you want in a WebJob. For more information about WebJobs, see Run background tasks with WebJobs.
Hope that helps. Please let us know if you have further questions.
-Grace