QB Issue Resolution:

Once you’ve downloaded and installed QuickBooks Desktop 2019, you can start using it right away. No need to wait until the new year.

John.Pero3276’s suggestions of checking your antivirus and pop up settings are a good place to start. There have also been reports of the activation process not working and our team is hard at work to get that taken care of. Don’t worry, in the meantime, there’s another way you can activate that involves a call into our team. An agent can help you get activated and work through any other trouble you’re having when trying to get into the program. The number to call is 1-877-772-9158 and agents are available 24 hours a day for Pro support.

Resolution for Issue 'can i start using 2019 to keep working in 2018 or do i wait until 1 jan/19?' available: Yes (Solved).
Source: Intuit Community forum.

can i start using 2019 to keep working in 2018 or do i wait until 1 jan/19?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for antivirus
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Error Recovery for antivirus [Canada]
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