Help calculating difference in time

SUMMARY:
I think I need something like this, but this function throws the error "Inconsistent formula":
=IF($B24="","",IF(OR($L24<=3,$L24="r"),IF($I24,TODAY()-$I24,"-"),IF($J24="-","-",$J24-$I24)))

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I have a spreadsheet laid out as follows:

Col B is "file name"
Col E is "age"
Col I is "date received"
Col J is "date closed"
Col L is "current status," with possible values 0-3 as well as some letters

I have a formula in Col E as follows:
=IF($B24="","",IF($L24<=3,IF($I24,TODAY()-$I24,"-"),IF($J24="-","-",$J24-$I24)))

The function works great almost every time. It tells me the age of the file from the time it was received to present--or to the date closed, if closed. When the case is open, Col L is a number. When the case is closed, Col L is a letter.

The problem is that in one scenario, the case is closed and Col L is letter "r". When this happens, the function flips out, and I'm getting a value of -41897.

I think I need something like this, but this function throws the error "Inconsistent formula":
=IF($B24="","",IF(OR($L24<=3,$L24="r"),IF($I24,TODAY()-$I24,"-"),IF($J24="-","-",$J24-$I24)))

Please assist. Thank you.