To enter tuplets in speedy entry, you need to first enter the notes, then convert them into a tuplet. If you're creating a tuplet at the END of a measure you can run into a situation where you need to "temporarily" enter more beats in the measure than the time signature will allow and Simple Entry may try to prevent you from overfilling the measure.

The trick is to turn off the "Check For Extra Notes" feature in the Simple Menu before entering the notes of the tuplet. (You may need to use the Redraw Screen command from the View menu to see the notes that do not rhythmically fit in the measure). Then select the Tuplet Tool and click on the first note of the tuplet to configure.

Once you're done you'll probably want to turn "Check for Extra Notes" feature back on to avoid accidentally overfilling any measures.