"unprecedented delay" is correct and usable in written English. It could be used to describe a situation when something is taking longer than usual or longer than expected. For example, "The unprecedented delay in the project's completion caused a lot of frustration among the team members.".
The unprecedented delay benefits no one who cares for justice.
The Ravens had pulled to a 28-6 lead over the San Francisco 49ers early in the third quarter when the power outage occurred, causing the unprecedented delay.
This unprecedented delay could have dangerous consequences not only because it creates uncertainty in our courts, but also because it undermines the traditions of our constitutional system of judicial succession for the highest court in the land.
On May 17, CSB Chairman, Dr. Rafael Moure-Erasentent a letter to Senate Environment and Public Works Committee Chair Barbara Boxer (D-CA) expressing frustration and concern about the "unprecedented delay and harmful delay" in granting members of the CSB investigative team access to the site.
The government seems unwilling to budge, and Labour has resorted to virtually unprecedented delaying tactics.
The same is repeated until the data reaches the final destination thus resulting in unprecedented delays.
In what one television executive called an unprecedented data delay, Nielsen Media Research failed to provide overnight TV ratings for four days this week.
When I feel like I can't trust my brain 100%, Ludwig really comes in handy. It makes me translate and proofread faster and my output more reliable.
Claudia Letizia
Head Translator and Proofreader @ organictranslations.eu