The phrase "extensive periods" is correct and usable in written English.
You can use it to refer to a period of time that is significantly longer than usual. For example, "The lawyer worked for extensive periods of time to prepare for the trial."
Several presidents spent extensive periods of time in the military, as well.
Some data sets range over extensive periods of time, and they have remained relevant.
Janet also studied people who had lost memory of extensive periods in the past, also without evidence of organic disorder.
To meet mission requirements they must therefore be operational for extensive periods of time.
These accidents, requiring extensive periods of convalescence and often painful treatments, left his legs atrophied and made walking most difficult.
In the following years the site was left unguarded for extensive periods of time and Skrunda-1 was stripped of everything of value.
The newly designed sand trap allows fully automated and high frequency measurement of sediment fluxes over extensive periods.
Even when the signal is removed, for example, by diluting a starved overnight culture in fresh medium, persister cells may still linger for extensive periods and be the ones found in the surviving fraction.
Mr. Mayer's manager, Michael McDonald, said that his doctors had been monitoring the growth for six months, and that it was only after extensive periods of rest failed to remedy the problem that he opted for surgery.
The Guardian exposed a series of incommunicado detention and abuse at the Chicago police facility, including people being held for extensive periods of time without public notifications to their families or access to attorneys.
Certain plant tissues can also stably store antigens for extensive periods of time at ambient temperatures, obviating the need for a cold-chain during vaccine storage and distribution, and so further limiting costs.
