If you belong to the VIP Gamer Club you can use the Pro performance option during off-peak hours and it will only take 1 SkyCredit per minute as if you were using the Gamer performance. This feature is one of the benefits of being the VIP member.
Here is a table with the off-peak times for each data center in UTC time zone and 12-hour clock format:
|Data Center||Off-Peak Time (UTC)|
|California||07:00 am - 01:00 am UTC|
|Washington DC||06:00 am - 12:00 midnight UTC|
|Dallas||05:00 am - 11:00 pm UTC|
|Frankfurt||01:00 am - 07:00 pm UTC|
|Hong Kong||07:00 pm - 01:00 pm UTC|
|London||09:00 pm - 05:00 pm UTC|
Again, those times are provided in the UTC time zone so depending on your location and time zone, they will be different for you and you will need to find out what those times are for your specific time zone. You should also see the indication of the off-peak time in the client whenever the off-peak rate applies.