It took us about a week, with occasional follow-ups. We started with 5 mins and increased it 5 mins more each night. Really once we got to 20 mins, it was sorted. As for the crying, believe me, one or two nights of 10 minutes of howling is wonderful compared to endless nights of bouts of crying every hour or so. Especially when the pay-off is setting the routine of full night's sleep. It sounds like you're about the time to wean the night feeds which will help too. As for the crying, I was gunshy about starting this process, it was my husband who insisted. However the first night, not even 3 minutes into the first 5, he cracked and begged me to let him run up to cuddle our daughter. It was funny. We waited for the 5 minutes and then soothed her, then left the room and did the timed responses as nessecary (which decreased as she tired out).
It's not as if you are leaving your baby to cry forever and being heartless and cruel. 5 minutes is not that long, and as long as he's crying you know he's alright, and you know that you will be going to him. Being a parent is partially about training behavior, and this is one of those instances. However you decide to deal with the transition, good luck!