OK, after a bit of research I've found that the reason behind the difference lies in.. milliseconds. Simple as that - Crystal truncates the time part of datetime to hours, minutes and seconds while SQL server keeps the whole "tail" of ms. So while the Crystal's version is wrong, in my case I had to fix the truth (SQL statement) to match the report by
SELECT convert (date, ENTERED),
count(distinct dateadd(millisecond, -datepart(millisecond, ENTRANCE), ENTRANCE))
FROM View1
GROUP by convert (date, ENTERED)
How to do the opposite (show the correct number from SQL in Crystal) still eludes me.