There are so many billions of types of bacterium in so many billions of environments that just to attempt an answer in full is problematic. What you're asking it seems is the mortality rate of antibiotic resistant bacterium prior to first reproduction.

The rate at which any bacterium multiplies varies since they utilize quorum sensing and multiply at different rates depending on their population. For this reason the population of this bacterium is important when asking the question. If the cell were in isolation or in a small colony it would almost certainly be in the lag phase: a phase of very slow growth as a bacterial colony begins establishing itself. Alternatively if the cell was part of a larger colony and had mutated antibiotic resistance while remaining sufficiently similar to its neighboring cells it would be in the log phase: a period of exponential growth after a critical population is achieved.

That's just its reproduction rate of the specific species and strain though, the probability of this cell surviving is based entirely on it's location. On agar in an ideal environment you could say that there is a 99.999% chance of this cell surviving. In other environments, particularly the environment of in infected human the probability of a single cell surviving within the colony is nearly impossible to determine as there are simply too many factors and very little data of this type. The question is interesting but simply unanswerable without at the very least a specific species, the gene used for antibiotic resistance (typically mecA), a simple environment for which similar test data exists, and the colonies size prior to the creation of the mutated cell.