"a definite timeline" is a correct and usable phrase in written English. You can use it when referring to a fixed timeline or schedule for something. For example: "We need to establish a definite timeline for the project in order to meet our deadline.".
But set a definite timeline for seeing improvement and then review the person's performance again.
"This gives a definite timeline," the Westfield superintendent, Margaret Dolan, said, noting the new one-day requirement.
"We're frustrated, like many of the citizens here, with not being able to get a definite timeline," said Lisa Vidrine, the director of St. Landry Parish's Department of Emergency Preparedness.
Ksander admitted his admiration for the aerospace engineers who build military technology: "Designing and building a B2 bomber, now that's a project!" A project must have a tangible outcome and a definite timeline.
Setting a more definite timeline for the Apple Watch does set expectations, however, ensuring that no one will be surprised when the wearable doesn't appear in March as rumored.
"It's all definite timelines," Reid is quoted as saying.
The company also recently raised a $60 million round led by Redpoint Ventures, with plans (but no definite timeline) for an IPO.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK