The phrase "active at a time" is correct and usable in written English.
It can be used to describe a specific period during which something is functioning or in operation.
Example: "The system is only active at a time when the server load is low to ensure optimal performance."
Alternatives: "operational during a period" or "functioning at a specific time".
Coordinated reciprocal switches in recombinase activity ensure that only one pair of recombinases is active at a time (Hallet et al, 1999).
Mr. Shields was active at a time when artists were reacting against abstract painting.
This generation of 'baby boomers' became sexually active at a time when the pill was only just making waves.
Over-privileged, nurtured in the heart of the establishment, personally appointed by Lord Kitchener, he was active at a time when his class still ruled half the world.
They were active at a time when the borough was falling apart, yet was nurturing dozens of artists, from photographers and painters to rappers and dancers.
Sidewinding allows minimal contact of the body with hot sand and thereby allows the snake to be active at a time when surface travel would be lethal.
Foursquare allows only one active special at a time, but some businesses rotate specials to keep offers fresh.
Let N 0 be the number of active neurons at a time point in the simulation.
Since it is known that in teleconferencing systems most of the conversations take place with one active talker at a time, the stereo perception can be easily realized by delaying and scaling a single signal.
Cryo-electron microscopy revealed that Rca docks onto Rubisco over one active site at a time, positioning the C-terminal strand of RbcL, which stabilizes the catalytic center, for access to the Rca hexamer pore.
Within the first year of signing up for the boards, I was maintaining several hundred active posts at a time.
