## 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 _date_from(self) -> Optional[Union[str, datetime.datetime]]:
        return self._data.get(DATE_FROM, None)
    @cached_property
    def _date_to(self) -> Optional[Union[str, datetime.datetime]]:
        return self._data.get(DATE_TO, None)
    @cached_property
    def date_from(self) -> Optional[datetime.datetime]:
        if self._date_from:
            if self._date_from == "all":
                return None
            elif isinstance(self._date_from, str):
                return relative_date_parse(self._date_from)
            else:
                return self._date_from
        return timezone.now().replace(hour=0, minute=0, second=0, microsecond=0) - relativedelta(days=7)
    @cached_property
    def date_to(self) -> datetime.datetime: