When you upgrade to VIP from a Zombies, Run! Abel Runner's Club subscription, you will be charged the full amount for a VIP subscription immediately. You will then be refunded for the amount of time remaining on your monthly or yearly Abel Runner's Club subscription on iOS, or charged a pro-rata rate on Android.
Your VIP subscription will last for a year from the date you purchased it on, and you will be charged again automatically on the renewal date.