The phrase "challenging timeline" is correct and usable in written English.
It can be used when discussing a schedule or deadline that is difficult to meet due to various factors.
Example: "We are facing a challenging timeline for the project, but I believe we can meet the deadline with hard work."
Alternatives: "difficult schedule" or "tight deadline."
The US Congress, through the Nasa Authorisation Act 2010, has mandated that this rocket should be launching by the end of 2016, although the agency has previously stated that it views this timeline as challenging.
At this time she has learned everything about our industry and she excelled in many client projects with difficult timelines and challenging client requests.
Any of the above reasons are challenging and valid and may increase your timeline for success.
Lawsuits challenging what the state does could also alter the timeline.
If the testimony did not fundamentally challenge the facts and timeline of the Benghazi attack and the administration's response to it, it vividly illustrated the anxiety of top State Department officials about how the events would be publicly portrayed.
On the latter, she explains how they challenged visitors to create a timeline of the date of arrival of various foods in the UK, looking at changes in the British diet since the year 1000 and the reasons behind them.
The progress report template, therefore, captures details on the progress of Fellows' work, timeline to completion, challenges faced (if any), any conferences attended or papers published, and expected date of graduation.
That seems to include the filmmakers, who canceled all interviews after Andrew Jarecki, the director, was challenged about having provided contradictory timelines.
A new analysis has challenged the accuracy of a climate timeline showing that recent global warming is unmatched for a thousand years.
Timeline Map could even challenge Foursquare's single player function of letting users keep track of their travels.
