Timeline view in Microsoft Planner

Your working account has an active premium trial; being in the same tenant and having similar roles does not automatically give your colleague the same entitlement. Timeline is a premium feature, so compare the two users' actual Planner subscriptions and trial status first.

Ask your administrator to check the affected user's assigned licenses and enabled services in Microsoft 365 admin center. Allowing self-service purchases or license requests permits a route to obtain access; it does not assign a premium license.

In Planner for the web, try My Plans, Create a plan, then a premium option. Microsoft documents this as another entry point for starting a trial or requesting a license. If the user already has a qualifying premium license, open a premium plan and check Timeline or the additional views menu.

If neither route appears, have the administrator raise a support request with both users' license details and screenshots.