There is no answer to your question
The doubling time of a bacterium is dependent on the conditions: primarily on the temperature and the availability of nutrients, but other factors can apply. Because of this, the doubling time of any particular bacterial strain cannot be considered in the abstract, thus to give a single number we can consider the optimum doubling time for a strain instead - i.e. how fast it will double under the perfect (for it) temperature and nutritional conditions. For the E. coli strain you worked with, this is likely 37 degrees and in a rich media such as Lysogeny Broth. But for the staggeringly vast array of bacteria out there, we simply don't know what the optimum conditions are much less have actually measured growth under them. In fact, there are many bacteria which are known about, but currently uncultured so we haven't even begun to understand their growth dynamics.
So even the simplified question of longest optimal doubling time cannot be answered because we don't have the data for so, so many bacteria. The question of the maximum time between divisions is even less clear: there are bacteria that live under conditions of extreme nutritional limitation that can take thousands of years to double, and strains that can exist as spores for at least 100,000 years and maybe even tens of millions. Do we consider their doubling time to be a 100,000 years? 25 million years? Without specifying the conditions under which the doubling takes place, the question is poorly defined.