Well, just follow that chart. If you need 18 peak objects you wait some time. For example, if this were in the Grassland area, then you wait 80 days, because on the 50th day they are times three. Therefore, 6*3=18. Only from 50 you have 18 objects, so from there you wait another 30 days, making a grand total of 80 days. Similarily, if it is the forest area, it is 90 days, Peak area 100 days, and water area 110 days. Or, the objects stay leveled that way, and so if you have already 50 days on your safari zone, you just put in 6 in for 30 days. That I am not that sure about tho. Serebii does really do a terrible job of explaning this...
Thats how I interpret it. I am sure my interpretation is correct, but I am not that sure. You would be better off getting one off the GTS or trading in the quick trade thread, rather than waiting 80-110 days. Anyone, if this is wrong, correct me ^^.