Hello and welcome,
How long it takes for an Ad Campaign to start?
As soon as your ads get approved, depending upon what ad scheduling you are using, Adwords would start delivering your ads on Google network. It also depends upon your billing status as well. If you have updated the billing details woth correct info, Adwords would review that as well.
Are your ads approved or still under review status?
Welcome to the community!
If everythings set perfectly fine like Billing Informations, Credit Amount, Kewords, ad-copies and landing pages adhere to Google AdWords Policy, your Campaign starts as soon as your ads are approved. It is stated that it takes 3 business days to get your ads approved but if everythings are fine it gets approved in hours.
I hope it helps.