What is the small amount of time during which the intention for ghusl may be made in advance, and can it be estimated by a specific duration?

The jurists have stipulated the permissibility of preceding ritual purity (tahara) with the intention (niyyah) by a short time, and it is obligatory to precede the first acts of purification with the intention. It is not permissible to precede it by a long time, according to the sound opinion of the madhhab. The reference for determining what constitutes a short or long time is common practice (urf).