ANSWER:

It is valid but he should avoid such gaps by either making his full ghusul first then shampooing after that or doing the shampooing first then his full ghusul after it.

QUESTION: A person took ghusl for 40 mins He poured some water on himself, then shampooed hair for 5-8 mins(water stop),then washed it, then he soaped body for about 10-12 mins, but maybe this gap can be longer as the Maths doesn’t add up to 40 then. Is the ghusl valid?