Unfortunately, If we are going to go with Roman time-keeping, we have to remember that the Romans did not have hours of standard length. To the Romans, there were 12 hours between sunrise and sunset, and 12 hours between sunset and sunrise. So, the length of an hour varied by date and latitude, and the length of an hour was different during the day and the night. Only on the equinoxes, would the Roman hours approximate our own.
So, if we use Roman time-keeping for Rivendell on October 25, and estimate that Rivendell is about the same latitude as Oxford, England. Then, on October 25, sunrise will be at 6:47 Greenwich Mean Time, and sunset at 4:50 GMT (ignoring the correction for the fact that Oxford is slightly west of Greenwich). Thus, each hour during the day would be 50.25 minutes long.
So, in Rivendell, 'nones', or the ninth hour during the Council of Elrond, would have started at 14:18pm our time. There would still not have been enough time to cram in the Council of Elrond.
Of course, we have no idea what time 'noon' meant in Elvish timekeeping. It could well be that the Elves used the term 'noon' to signify the start of twilight? (A significant time for them.) Still, JRRT, translating into English, would probably have used some different term if he understood the time of the bell to be anything other than mid-day.
Now, in my opinion, there is no way the Council could have been concluded between its start, and solar noon. (The start must have been what? 8:00? 8:30 at the earliest? Frodo watched the sun rise above the Misty Mountains (later than it would have risen over a flat horizon) before attending the Council, and at the start of the Council, "The light of the clear autumn morning was now glowing in the valley". For the sun to have got that high after a 6:47 sunrise, must have taken more than an hour?) . The Council just cannot be done in 3.5 or 4 hours. If the Elves used (for some reason) Roman time, adding another 2 hours 18 minutes still wouldn't do it in my opinion.
Could it be that the power of Elrond, through his Ring, managed to slow time? Slowing time is a very Elvish and Elvish Ring desire? Galadriel manages to manipulate at least the perception of time, later in Lothlorien.
Did 'noon' mean 'solar noon' (as should be if JRRT's translation was good)? Did Elrond manage to slow time so that at least 8 hours of Council were packed in between 8:00 and 12:00? Could it be that the effect was so subtle that almost no one noticed? Was only Bilbo's belly immune from the effect? When Bilbo made his plea for lunch, was that because in the un-spelled world, it really would have been noon? After that, the Council had to get through Bilbo's tale (without omitting a single riddle); Frodo's tale (with interruptions and questions) Gandalf's tale; and then the whole discussion. That had to take at least 4 hours in normal time? Maybe more?