It is true that Google Ads PPC provides instant results as compared to any other digital medium of lead generation. However, it is absolutely wrong on the part of advertisers to believe that a Google Ads PPC campaign need to be launched on the very day when they need it most - may it be a product launch, project launch or any offer announcement.
Once the campaign is launched it needs regular careful monitoring, research & optimization. A campaign starts getting on track in 1 - 2 weeks of time and can deliver the best of results only after a month of efforts. So it's always advisable to start a Google ads ppc campaign minimum two weeks in advance (preferably a month) before the actual show date / period.