There are many ways to be able to add time and/or game time offers within the web admin. Here are the different ways which you can do so:
To add time to an existing user, search for them in the Dashboard (search field is located in the upper right side of the screen). Once you see the user that you want, click the "more options" (three dots) button and you can add offers through "Quicksell". Do note that offers with Available for quick sale enabled are the only ones that will show up in "Quicksell".
From the User Profile
You can also add time by going to the user's profile. From there you can click "Start shopping" which is located in the upper right side of the screen or if you have Legacy mode enabled, you can select "Add time" from the option in the Time section of the user's profile.
Via A Logged In PC
You can add time directly on the PC Dashboard by clicking the username that is logged in on the PC. A dropdown menu will appear where you can select "Quicksell", "Shop", "Add/Remove time", or "View Profile".
Alternatively, if you have graphical view enabled in the PC Dashboard, you will need to click the node where the user is logged in. Then click the username in the dropdown menu which in turn will open another menu where you can select "Quicksell", "Shop", "Add/Remove time", or "View Profile".