"unduly long" is a correct and usable phrase in written and spoken English.
It simply means "unreasonably long" or "excessively long". For example, you might say, "I believe the meeting was unduly long and could have been concluded in less time."
Check your notice is not unduly long or short.
Collegiate planning can be unduly long and cumbersome, generating voluminous reports that amount more to a "wish list" than a set of strategic choices.
Namely, it was argued that patents were invalid, that Smartflash waited unduly long to file a case and that it did not have ultimate control over the patents.
His published essays — refined and expanded versions of the lectures — can seem unduly long and, once read, slippery in the mind.
It quickly eliminated all unnecessary ones and shortened those that were unduly long, which forced people to maximize output per minute of meeting time.
Prison terms, though reduced, remain unduly long, meaning that thousands of minor drug offenders will still be incarcerated for excessive lengths of time.
It does not unduly damage the long term investment case for ITIS in our view.
Even the great social and political upheavals that accompanied the advent of the Iron Age did not unduly disturb their long-standing and highly specialized relationship with the tropical environment.
However, because Polypodium and myxozoans have unusually high divergence rates in their 18S rDNA sequences, these cladistic analyses have been criticized by a number of authors who suggest that the data might be unduly affected by long-branch attraction (LBA) [ 5, 21, 22].
But options, it turned out, encouraged managers to take unduly big risks, as long as they showed handsome short-term profits.
Other phase of the mystery are that none of his family became unduly alarmed for a long time; a breach of promise suit by a Miss Lawrence Fay against him was filed same day he disappeared.
