how to compare posts with array

im setting up custom theme for real estate. idea is that the listing is obtained with json from application server and im cool with this part.

on the init ill populate database and turn all listings as wp posts. now i have little problem as im not sure how to deal with udate… i can count elements in array and compare with count from last update and then mark new ids for wp_insert.

the array is like 0 = > id, date of update and im thinking to put that lsat udate date as meta info attached to post. there would be a script set under cron to run this php every hour or so. im just not quite sure how to perform:

for each offer in array{
compare date change with posts where id = customf_id and update customf_date
}

and most of all is it server efficent… could any1 propose good idea how this could be dealt with?