Possible Clues:

• Time of equal day and night length
• Astronomical phenomenon largely affecting horse and bullock
• When night=day in length
• When night and day are of equal length
• March event
• Time of the year when night and day are equal
• Start to spring astronomically almost like horse and bovine
• When its almost horsey before its beastly
• When night and day are equal
• Day with 12 hours of light