I'm constructing a spreadsheet that uses time entries such
as 11:00, 11:00A, 11:00B, etc. How do I create a formula
that I can use to sum all of these entries in a range?

If all your entries (including the 11:00) are text, and if times before
10:00 are formatted with leading zeros, then try this...

=SUM(TIMEVALUE(LEFT(A12:A14,4)))

You would commit this formula by using Ctrl+Shift+Enter (not just Enter by
itself).

If you have some different conditions than assumed above, please tell us
what they are.

Rick