Bridge demolition

My next scheduled game: "The crossing point at Kösen" is based upon an engagement around a bridge over the Saale River that the French want to demolish whereas the Austrians need it in good shape to pursue the defeated Grande Armee. A question arose during the design: what's the time span needed to demolish (blow up) a permanent bridge?The author of the 'Programmed Wargame Scenarios', C.S. Grant, did not give any clue about that topic, but in the 'Notes on bridge demolition' (accompanying 'The bridge' scenario in the same book) he indicates that 5 hours were needed to make the plans for demolition.A search for more information lead to Napoleon-Series Forum where Ned Zuparko provided the following info:
"Charles Totten's 1880 "Strategos: A Series of American games of War Based upon Military Principles..." In Volume II, pg 23, Table G ("Time required for various purposes) includes:
98. Destroying a pile bridge........... 2 to 6 hours
99. Burning a wooden bridge (esch 50'), Case 5 Table II................ 30 to sixty minutes
100. Extinguishing same, if possible (after 20 minutes, 10:1 against) 15 min- 1 hour"In Google books I carried out an Advanced Search with bridge demolition. The best result was: Aide-mémoire to the Military Sciences: Framed from Contributions of Officers... where some useful information was found but not about the necessary time span. After several attempts I discovered American Kriegsspiel (p.124)"DESTRUCTION OF BRIDGES AND FORDS.
§ 264. When four three-inch guns fire upon a bridge 1,000 yards distant with shells it will in the general case be destroyed in about 10 or 15 minutes.
§ 265. A wooden bridge is rendered impassable by tearing up the planks in 15 or 20 minutes; a brick or stone bridge in 30 minutes or 1 hour. To burn a wooden bridge at least haif an hour’s preparation is required. To prepare to blow up a wooden bridge at a particular time, 90 minutes; a brick or stone bridge, 2 or 3 hours.
A ford may sometimes be destroyed in 1 or 2 hours"
So the consensus lies from 2 to 6 hours with the older sources giving smaller time spans. The mechanism finally incorporated in the Scenario was:

The sapper detachment accompanying the French force must be in contact with the bridge. Then, 4D6 are thrown and their sum is the number of (10 minutes) turns that sappers must be in contact with the bridge to demolish it. If the contact is lost for more than 3 turns, an additional D6 must be thrown.
In that way a pseudo-gaussian probability of distribution is found with a maximu likelyhood centered at 14 turns, i.e. 2 hours and 20 minutes. The play-testing will say if this was a correct estimation or not!