I GOT TOLD THE 12TH DAY, BUT MY FRIEND SAYS DIFFERENT. HELP PLEASE

Every bitch is different some are as early as 2 days others can be 20+ days.
the norm is 10 and 12 or 11 and 13.

Usually 11th and 13th day.  My Spanish usually the 18th day!!!!  All dogs are different, that's why it's good if the owner of the stud can have the bitch or if you are able to drive down on a number of occasions. 

The best day to mate if only having one mating is two days after ovulation as the eggs don't ripen and are not ferilizable until then, and they then die within another two days.  the problem is different bitches and even the same bitch in different seasons ovulate on different days.

Day 12 and 13 for a lot of bitches in my breed and especially my own would be too early.

When I ahve done premate tests these have shown they don't ovulate until about day 12 so for them day 14 to 16 would be best,a nd I ahve had the largest liters and no misses when I ahve mated on day 15 but have had bitches miss or ahve small litters if they started being mated at day 10 to 12.

Find out from your bitches breeder what days her mother and granmother were usually ready, the stud dog woner will also know what is usual within your breed, but bitches as ididvisuals may be ready any time as early as day 7 and as late as day 27!