it starts almost instantly instantly but may take 0-24 hours normally depending on big giants systems, aol dns servers updates in 24 hours, I read it used to be a week for updating 10 years before, it was horrible. I suggest u a better way, Go change only A record in your present DNS records and let your files reside on current box too, then you will never feel any delay. because its will be like HA solution in that case.
used to take 24 hours to propogate - i only use namecheap. but it has been less than 30 minutes quite a while ago.
DNS update time varies vastly. You'll just have to accept whatever time it updates as the time it updates, simple as that.
normal time is upto 48 hours some times it will work fine for u but it may not work for few countrys. so DNS to spread worldwide it takes max 48 hours.Ya namecheap is very quick it is almost instalt for me so i preff NC.
Depends on your registrar, usually no more than 48 hours. Your ISP may use cached DNS servers, so may see the old site. Try tools like dnsstuff.com to check on its progress.