A �wink' has meant a short nap since the 1300s, appearing as such in Langland's Piers Ploughman, for example.
�40' was a common figure chosen to mean an indeterminate number in past times...eg Jesus' 40 days in the wilderness, the idea that - if it rains on St Swithin's Day - it will rain for 40 days and 40 nights, Ali Baba and the 40 thieves, our word �quarantine' comes from the French for forty and so on.
I also suspect the �40' here might refer to the number of minutes involved, since 40 of them seem ideal. Any fewer and it does not fulfil its purpose of refreshing you and any more just leaves you feeling even more tired, in my experience.