and some say three hours three minutes !
or 115 days.
If you have a definite mating date, then it is highly likely that your pig will go a max two days either side - it is very rare (rare = it does happen, very rare = someone on the forum will have an exception)) to be earlier or later than this, as I say IF you have a definite mating date ie seen full lock and hold.
Most of our sows farrow early or late evening - normally just as suppers ready, or just as you're ready for bed
- some you will find had or are having when you get up, but whilst they can have at anytime it is uncommon in the middle of the day (uncommon - yes it does happen - for us maybe 1 in 25)