What is this time? (Analog Timing)
Der Bus kommt um fünf vor drei Viertel .
This means 5 minutes before a quarter to something, which boils down to:
xx:40 Uhr
The hour was already missing from your question. Only in some regions times are given with dreiviertel, and more typically no further modification takes place for those. If modification would be necessary the time specification would change to
20 [Minuten] vor [insert hour]