awk. How I missed you.

awk </dev/null \
'END { for (i=0; i <13 ;i++) \
{ printf("%02d:00-%02d:30\n%02d:30-%02d:00\n", i, i, i, i+1) }}'

The output was pasted into a spreadsheet.

I don't think this is how the creators of the original spreadsheet imaged things.