The 710–2 is a soft collar with a gentler degree of stabilization, and the product information describes it for short-term wear in suitable situations. It is not meant to be worn around the clock, and for a child every wearing session should happen under adult supervision.
Typical use for this category of product is limited periods: during prolonged sitting, after physical strain, or during a calmer rest period when the neck feels overloaded. A practical way to start is with short sessions of roughly half an hour, so both you and the child can judge whether the fit is comfortable and the collar stays in place. If the use is part of a recovery plan recommended by a specialist, follow their wearing-time instruction instead of a general guideline.
Take the collar off for eating and for any activity where a firm object around the neck could be unsafe, such as active play or sports. Watch for signs that a session has lasted too long: the child repeatedly pulling at the collar, complaints of pressure under the chin, or reddened skin along the edges. If neck symptoms are strong, persistent, or related to a trauma, do not decide wearing times on your own — consult a specialist.