The phrase "a time of substantial" is correct and usable in written English.
It can be used to describe a period characterized by significant events, changes, or developments.
Example: "The company experienced a time of substantial growth after launching its new product line."
Alternatives: "a period of considerable" or "an era of significant".
Others would call for new commitments of money at a time of substantial budget deficits.
Interest in producing paper books comes at a time of substantial growth in the electronic book industry.
"The late 1200s was a time of substantial social, political and religious ferment and experimentation," said William D. Lipe, an archaeologist at Washington State University.
But the handoff also meant that Mr. Bernanke would face murkier choices at a time of substantial risks that increase the chances for serious missteps.
Not only has this goal not been achieved, but the United States has become isolated from the people of Cuba as well, at a time of substantial change on the island.
But then this is a time of substantial political and cultural shift, with the Social Democrats adopting many pro-business measures and many Germans developing a sudden infatuation with the Internet.
Kurt Lambeck, president of the Australian Academy of Science, said the 25% budget increase was "substantial at a time of restraint".
There was a time when a substantial portion of the population was in domestic service.
Hereafter, a time period of no substantial temperature change is referred to as epoch.
In a short period of time a substantial number of patients were included, which demonstrates the feasibility of this novel technique.
(1)– (3) Although this has been found beneficial for patients with particular tumors – albeit only for a limited duration of time – a substantial fraction of patients with cancer proves to be finally resistant to VEGF-based therapies.
