The phrase 'fluctuate from time to time' is correct and usable in written English. You can use this phrase to describe situations or things that experience varying amounts of success or change in cycles or intervals. For example: "My son's grades seem to fluctuate from time to time, so I keep a close eye on his academic performance.".
The exchange rate between any two currencies was a market rate that fluctuated from time to time.
Commodities are identical units of sure value — bushels of wheat, say — whose price fluctuates from time to time and place to place.
In these tests, the colony numbers fluctuated from time to time.
Since they are salable, their price fluctuates from time to time, going above maturity value when the current market interest rate falls below the interest rate that they bear and falling below the maturity value when the current rate rises or when fear about the ability of the government to pay interest develops.
For example, when demand for a product is high enough to justify continuous production, the production level might need to be adjusted from time to time to address fluctuating demand or changes in a company's market share.
Second, consciousness levels may fluctuate even in the short period and scores may therefore be different from time to time.
From time to time.
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