Install Time in Status Plugin for Jira Server/Data Center

Install from Atlassian Marketplace

Log in to your Jira instance as an admin.
Click the profile icon on the top right-hand corner of the screen.
Go to Atlassian Marketplace.
Click Find New Apps on the menu on the left-hand side.
Find Time in status | SLA | Timer | Stopwatch via search.
Click Buy Now to purchase a license for "Time in status | SLA | Timer | Stopwatch" or Free Trial if you want to start a trial.
If you have clicked Buy Now, then the Atlassian Marketplace checkout page will appear. After you have purchased a license, click Apply License.
If you have clicked Free Trial, then the Free Trial screen will pop up. Click Get License.
You will then see the my.atlassian.com login page.
Log in to my.atlassian.com.
Click Apply License.

Open plugin page on Atlassian Marketplace: Time in status | SLA | Timer | Stopwatch
Select hosting: Server or Data Center.
Click Download at the bottom of the page.
Log in to your Jira instance as an admin.
Click the Administration icon on the top right-hand corner of the screen.
Go to Manage apps.
Click Upload app.
Click Choose file and select the downloaded file.
Click Upload.
Activate a license for Time in status | SLA | Timer | Stopwatch or Free Trial if you want to start a trial.
If you have clicked Buy Now, then the Atlassian Marketplace checkout page will appear. After you have purchased a license, click Apply License.
If you have clicked Free Trial, then the Free Trial screen will pop up. Click Get License.
You will then see the my.atlassian.com login page.
Log in to my.atlassian.com.
Click Apply License.