I can not explain why {Use EDUs for Beat Duration} is “un-checkable” in your copy of Finale.

However, the Time Signature Tool is a very powerful tool, with many ways to enter a time signature.

Work smarter, not harder!

The option {Use EDUs for Beat Duration} is very seldom the smartest way to enter a time signature.

My guess is that you can get, what you need, in a smarter, faster way.

* What time signatures do you need?

Please explain.

The better we understand, the better we can help.

Thanks!
Is there another way to set a meter of 7\8 with a subdivision (beaming) of dotted quarter, then two quarter (and on top of that, a 9\8 meter in the next bar, also with a dotted-quarter-based subdivision)?  

1) To set a time signature of 7/8 beamed as 3+2+2,

either

- (smart and fast) use the context menu,

or

- (with a deeper understanding) in the dialog box Composite Time Signature, enter

3+2+2 in the first field (yes, that is right: enter five characters in one field!)

over

8

Back in the dialog box Time Signature the “real” time signature will now show as 3+2+2 over 8.

To get a “display” time signature of 7/8, click the button {More Options}, to expand the dialog box downwards.

2) To set a time signature of 9/8 beamed as 3+3+3, there is no need for the dialog box Composite Time Signature.

Either

- use the context menu

or

- in the dialog box Time Signature, set the Number of Beats to 3, and set the Beat Duration to a Dotted Quarter.

3) In the Composite Time Signature the method

3+2+2

over

8

could be called the “Numerator” method.

Just for the fun of it (and for the understanding), also try the “Denominator” method:

1 over 4+8

plus

1 over 4

plus

1 over 4

For more fun, try using numerator decimal numbers:

0.875

over

1

will beam all seven eighths together.

Thanks Peter, for your enlightening answer! Been using finale for years and never thought there's an elegant way not to have to use EDU's. As for the part of my question in the bracket, I'm afraid I wasn't clear enough - as there an elegant smart way of setting alternating time meters (i.e. 7\8 in bars 1, 3, 5, 7 etc. and 9\8 in bars 2, 4, 6, 8 etc.) or should I just create two bars with altering meters and manually copy-paste those all across the document? 

… is there an elegant smart way of setting alternating time meters (i.e. 7\8 in bars 1, 3, 5, 7 etc. and 9\8 in bars 2, 4, 6, 8 etc.) or should I just create two bars with altering meters and manually copy-paste those all across the document? …

Just create the first two measures, then “manually” copy the two measures a “gazillion” time across the entire document.

To do so - at one fell swoop - use the command Paste Multiple:

1) Selection Tool, select the two measures.

2) Hold down CTRL and ALT, and click the following measure.