SeyYes
Actually they say at once, which in basic english means immediately. Hence the break down, each month is an instant 500 with 310 spread over the average 28 to 31 days.
You have to look at the top ups as well, if it was 500 only the first month that means you pay 9.99 a month for 310 coins which is highway robbery since the basic coin top up package costs less for more coins, there'd be no benefit at all of buying membership.