What is the maximum time jira takes to respond when cloud instance is having heavy load

[jagadeesh madhura]

I want to understand how jira works, is there any limit of number of projects creation, is there any api limit for each cloud instance

It has been more than an hour, still I'm not able to access my cloud instance, getting error 

{"errorMessages":["This Jira instance is currently under heavy load and is not able to process your request. Try again in a few seconds.

rest/api/2/project doesn't give response consistently, and fails because of the above error, we have around 3670 projects

[Brant Schroeder]

This is the last information Atlassian provided in late 2019.  I have not seen an update since this came out so I am assuming it is the same.

In Jira Cloud we use rate limiting for REST API to protect our customers’ sites (aka tenants) resources. Current implementation isn’t based on REST API consumer, it is based on concurrent requests made across all consumers of single tenant - consider tenant users, your App and other Apps accessing the infrastructure. Thus it is a challenge to provide meaningful, guaranteed information for consumer in response headers (e.g. Retry-After), such information could be seen only as a suggestion.

In case of implementing retries please be advised of using back-off mechanism to lower retry frequency on subsequent failed attempts and increase traffic gradually on a success. Concurrency based limiting is more visible for longer requests so the rule of thumb would be the longer request is the lower concurrency should be used.

We are actively working on per consumer rate limiting which should help us provide meaningful information in response headers. We expect it to be delivered in couple of quarters.

[Daniel Ebers]

Except for the limits mentioned on the page for free plans and the information Brant gave about API access I cannot recognize any limits for your project (for example the number of projects itself).

For me it looks like there have been to many requests to REST API which might result in the error message you got this day.

Cheers,
Daniel