## Is your feature request related to a problem?

#4947 added a new query to the backend – time to convert. It works well, just one point is kind of rough: bin width and count.

## Describe the solution you'd like

Currently the number of bins is hardcoded. Ideally we should have two options:
- return a user-specified number of bins,
- otherwise infer a reasonable number of bins using some algorithm (auto option).

@alexkim205 [suggested](https://github.com/PostHog/posthog/issues/4855#issuecomment-872423877) the [Freedman-Diaconis rule](https://en.wikipedia.org/wiki/Freedman%E2%80%93Diaconis_rule) for determining bin width (and interval based on that), but unfortunately from my testing its formula would not be the most practical – it's great for keeping a pretty constant "smoothness" of the histogram esp. with normal distribution, but we face some additional constraints that make it less than ideal:
- we can't have histograms too dense visually in the UI, from my testing a practical limit is 60 bins (above that it gets too dense),
- our data generally doesn't follow much of a normal distribution.

Clamping may help though, or maybe a different formula may work better outright – I'll be testing this.

## Additional context

Issue pertaining to the experience of time to convert: #4855

#### *Thank you* for your feature request – we love each and every one!

posthog/models/filters/mixins/common.py
@cached_property
    def breakdown_type(self) -> Optional[str]:
        return self._data.get(BREAKDOWN_TYPE, None)
    @include_dict
    def breakdown_type_to_dict(self):
        return {"breakdown_type": self.breakdown_type} if self.breakdown_type else {}
class BreakdownValueMixin(BaseParamMixin):
    @cached_property
    def breakdown_value(self) -> Optional[str]:
        return self._data.get(BREAKDOWN_VALUE, None)
    @include_dict
    def breakdown_value_to_dict(self):
        return {"breakdown_value": self.breakdown_value} if self.breakdown_value else {}
class InsightMixin(BaseParamMixin):
    @cached_property
    def insight(self) -> str:
        return self._data.get(INSIGHT, INSIGHT_TRENDS)
    @include_dict
    def insight_to_dict(self):
        return {"insight": self.insight} if self.insight else {}
class DisplayDerivedMixin(InsightMixin):
    @cached_property
    def display(self) -> str:
        return self._data.get(DISPLAY, INSIGHT_TO_DISPLAY[self.insight])
    @include_dict
    def display_to_dict(self):
        return {"display": self.display} if self.display else {}
class SessionMixin(BaseParamMixin):