This really depends on the scope of the campaign, but most campaigns take 2-4 weeks to get started.
There are parts of new campaigns where we'll require your input or work: getting access to different software (Analytics, Tag Manager, Website Logins, etc.), landing pages prepared, email campaigns prepared, etc. – in 98% of cases, it's providing these resources to us that slows down the start of a campaign.
Please see What do you need to provide BEFORE I can launch a new PPC campaign? for more information on what you'll need to provide. Beyond that, we'll create a timeline for the launch of our campaign with clearer expectations for you.