I should point out that there's a similar application from the same developer called 'Silent mode timer widget' (go on, have a guess what it does!), just in case you need that profile rather than offline...
Using this is simplicity itself, as you might imagine. Rather than setting 'offline' mode in the traditional way, you tap on the right side of the widget to set the timer and then tap on the left side to activate it. 'Offline' profile is then immediately in effect, and after the appropriate time limit, your original profile is restored. Meaning that you don't have to remember to change it back yourself. Phew!
Inserting the widget from the 'Add widget' list on the homescreen; setting the timer (in this case for 2 hours)
Very handy and well worth a quid to me, at least. See also the developer's other titles in the store, there are quite a few widgets of interest.
You can buy Offline timer mode widget from the Nokia Store for £1 here.