compare date fields

I can’t figure out the exact format to compare two date fields. The dates are stored in timestamp format. I need an “if” – the end date is greater than the start date by more than 86399 seconds, i.e. the next day. (I’m calling Events Calendar posts, which used to calculate the EventDuration and seems to have stopped!) Or, a way to calculate the event duration and pass that to the loop.
Please help! Thanks Susan