The part of the sentence "vary from time to time" is a correct and usable phrase in written English. You can use this phrase to indicate that something does not always remain the same, but is subject to change. For example, "The prices of our products vary from time to time, so please check the website for the most current information."
Vouchers can only be used for Masterclasses courses and seminars which may vary from time to time.
Like any price, it should vary from time to time, and maybe it should vary in predictable ways.
The number of troops in a brigade can vary from time to time, meaning that the extra deployment could be anything between 30,000 and 35,000.
Although water is most often taken from a safe municipal supply, it usually is processed further to ensure uniformity of the finished product; the amount of impurities in the municipal supply may vary from time to time.
The cost of your subscription will be made clear to you on our sign-up pages and in your welcome email and may vary from time to time or by country.
A look at land regimes in the earliest periods of human history can illuminate debate over the extent to which human institutions can be expected to vary from time to time and place to place.
It varied from time to time.
The festival's many traditional contests were also varied from time to time by cultural events.
It varies from time to time in a person's life, and from person to person as well".
The crime rate measures the amount of crime people are suffering from, he said, while the prison count is a measure of how severely society chooses to deal with crime, which varies from time to time.
The purpose and/or motive varied from time to time but the effect of the false submissions was to render the rates unreliable, if not meaningless, and to undermine the integrity of Libor as a benchmark".
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