[ahmadfaruq]

It is makrûh to eat something or to sleep in a mosque. A musâfir is exempted from this. When entering a mosque, a musâfir must intend for I’tikâf and perform the namâz of tahiyyatulmasjîd first. Thereafter he can eat and talk about worldly matters.

[Rida]

Shaykh Hussain once said that you everyone should make an intention for a nafl itikaaf anytime they enter the prayer area of a masjid. This way they can rest or do other stuff without any worries. There is no time restriction on it either. You can stay for 5 minutes or 5 days etc..

Wassalaam