Those dropdowns  are populated programmatically from a sealed class that
Microsoft built. The only way you might be able to remove  individual entries
would be to write a Javascript that would remove them when the page is sent to
the client.

Know of any examples of code to do this?

Sorry, no I don't. But I did see one in the past that changed the formatting of
individual tabs in the top nav bar, even though they are generated by a single
server control. So it should be possible. I've lost track of that code though
also and Java isn't one of my strong areas.

I whipped up a little something that works in the calendar  NewForm
page. It's fairly static, but can be changed easily and it should do
exactly what you want.

function RemoveTimeSlots() {

// Get all the dropdownlist elements in the page.
var oTime=document.getElementsByTagName("select");
var iT=0;

// Loop through the dropdowns  to find the ones you need to change.
for(iT=0;iT<oTime.length;iT++) {
// Identify all the dropdowns that assign hours).
if(oTime[iT].id.indexOf("DateTimeFieldDateHours")>0) {
/*
This removes the 3PM and 4PM items, but you can easily change that
or
all parameters to the function to make it more dynamic.
*/
oTime[iT].options[16]=null;
oTime[iT].options[15]=null;
}
}
}