On average, how long is the old English time unit a "moment"?

A moment (momentum) was a medieval unit of time. The movement of a shadow on a sundial covered 40 moments in a solar hour. An hour in this case means one twelfth of the period between sunrise and sunset. The length of a solar hour depended on the length of the day, which in turn varied with the season, so the length of a moment in modern seconds was not fixed, but on average, a moment corresponds to 90 seconds. A day was divided into 24 hours of both equal and unequal lengths, the former being called natural or equinoctial, and the latter artificial. The hour was divided into four 'puncta' (quarter-hours), ten 'minuta', or 40 'momenta'.

The earliest reference we have to the moment is from the 8th century writings of the Venerable Bede, who describes the system as 1 hour = 4 points = 5 lunar points = 10 minutes = 15 parts = 40 moments.

The unit was used by medieval computists before the introduction of the mechanical clock and the base 60 system in the late 13th century. The unit would not have been used in everyday life. For medieval commoners the main marker of the passage of time was the call to prayer at intervals throughout the day.