Amazon make listings active and deactive via cron job

We currently have a script which seems to have become very unreliable so we would like a new one, from scratch would be best. We have fulfilled by merchant listings which we would like activated at 6pm, and deactivated at 6am by cron job. It is only certain SKUs, and it is important that the quantities are recorded, so they are accurately reactivated at 6pm. E,g SKU TEST3939 Quanitity 6 This activates at 6pm and will sell over night. by 6AM there are only 3 items left (active items report), so the sku and quantity 3 are stored and quantity 0 is uploaded for this sku. Then at 6PM the quantitiy 3 is uploaded again. This will only apply to some skus, not all in the inventory. The script we have which performs this task currently occasionally gets the error below and fails. As there is not an if error clause in the script, it then stores 0 as the quantity for all skus and when it comes to reactivate it again, all the stock is set to 0. We need to prevent this in the future: "Sender RequestExpired Request signature is for too far in the future. Timestamp date: 2014-09-12T12:23:09-04:00. Currently, 5 percent of requests that are more than 15 minutes in the future will be rejected. b50ea741-3256-4cca-9b2e" If you can create this script please let us know. We would like it to run via cron from our server each day. Thanks