The phrase "are essential when the" is correct and usable in written English.
It can be used to indicate the importance of something in a specific context or situation.
Example: "These resources are essential when the project deadline is approaching."
Alternatives: "are crucial when the" or "are vital when the".
As I'm follically challenged, hats are essential when the temperature plummets.
Open IE approaches are essential when the number of relations of interest is massive or unknown.
Controlled release dosage forms are essential when the drug release rate impacts the effectiveness of therapy.
Such studies are essential when the target is tumour blood vessels, as preclinical studies showed minimal tumour size reduction when vascular targeting drugs were given alone.
Utility values for exacerbated COPD based on generic instruments are essential when the cost-effectiveness of interventions is to be assessed that reduce the frequency or severity of exacerbations in COPD.
Mammalian cell-based expression systems are essential when the protein of interest cannot be expressed in bacterial- or yeast-based systems and/or when conventional glycosylation is needed for the folding or stability of the protein (reviewed in [ 4]).
They provide a safe neutral space for people to look for work and they'll be essential when the government enforces online benefit application.
All this sounds hopelessly technical; in fact, colossal human issues are at stake, because a complete understanding of the minutiae will be essential when the time comes for the Colombian people to validate these agreements.
Pathogen isolation by bone culture is essential when the patient is treated with ATB only.
Evaluation of head-position dependency during the ice-water test is essential when the test is indicated.
This is essential when the purpose is to keep the historical memory of different population in relation to facts or experiences from the past.
