The phrase "are most important when" is correct and usable in written English.
It can be used to emphasize the significance of certain factors or conditions in a specific context or situation.
Example: "The safety protocols are most important when conducting experiments in the laboratory."
Alternatives: "are crucial during" or "matter most in".
are most important when wages are relatively low during youth and old age.
This methodology includes considerations which are most important when deciding on an approach to resilience.
BT: And it's a good column because it makes you realize that, as you say, these issues are most important when they're the most difficult.
This article reports a study designed to identify the factors that both hiring bodies and applicants believe are most important when making decisions about principal selection, appointment and acceptance.
Box's exciting milestone (and my new start at Infer) have led me to reflect on the mindsets, strategies and playbooks that are most important when setting the stage for unicorn-like rapid growth.
Lazear pointedly stated that he expects strong growth due to high productivity and low taxes, adding that "two trends are most important when looking at last year's economic picture and the scene as we move into 2007″ the labor market and export growth.
This relationship is most important when an issue arises specifically because someone is part of the way through transition.
In fact, understanding may be most important when you face issues that cannot be easily resolved, such as different religious or political views.
For observant Muslim women, covering up the body is most important when they are in the company of non-mahram males, those not related by blood or marriage.
And — and this might be most important — when they sensed proud Pittsburgh was wounded, they tore at the Penguins' festering flesh, spitting on them for good measure.
