You report the moving expenses when you pay them, assuming it is a qualified move.  (New job more than 50 miles from your old home, job will last longer than 39 weeks).  Expenses are deductible when paid up to one year before to one year after the start date at the new job. 

If the move later becomes non-qualifying (you quit or are fired and move back before the minimum time) you will make an adjustment on next year's tax return.