Hi there! It’s actually not so trivial with formulas only. Here’s how I have done it:

First, we need the days until next Friday, next Saturday and total amount of days between two dates (our two date fields are called ‘Start’ and 'End; calculations done in three separate fields).

Time until next Friday ({TnF}): `IF(WEEKDAY(Start)>5, 12-WEEKDAY(Start), 5-WEEKDAY(Start))`

Time until next Saturday ({TnS}): `IF(WEEKDAY(Start)>6, 13-WEEKDAY(Start), 6-WEEKDAY(Start))`

Total amount of days ({StE}): `DATETIME_DIFF(End, Start, 'days')`

Now we can calculate how many Fridays and Saturdays there are between the two dates (done in separate fields).

{How many Fridays?}: `IF(StE<TnF, 0, IF(StE=TnF, 1, ROUNDDOWN(((StE-TnF)/7),0)+1))`

{How many Saturdays?}: `IF(StE<TnS, 0, IF(StE=TnS, 1, ROUNDDOWN(((StE-TnS)/7),0)+1))`

And now we can subtract Fridays and Saturdays from the total date difference in days:

```
StE-{How many Fridays?}-{How many Saturdays}
```

Maybe someone comes up with an easier way, but this works