Julie here from Shopify Support. Thanks for reaching out!
To clarify, are you curious about Virtooal's billing cycles? Based on what I'm seeing on both of their apps' pages in the Shopify App Store (here and here), they bill their users monthly. However, it looks like they offer a discount if you choose to pay annually. They also have some information about billing over in the Virtooal Knowledge Base.
That being said, it's best that you reach out to the app developers directly should you have any further questions; when it comes to third-party apps, the developers themselves are responsible for determining how their apps are billed. You can typically find their contact information directly within the app itself, or under the Support section of their app page in the Shopify App Store. We also have information on getting help with third-party apps that you should find insightful.
If you're looking for more general information on how third-party apps are billed, however, then it might be worth checking out our help doc on app charges. There, you'll learn about different types of app charges, app billing cycles, and how apps are billed along with Shopify's monthly subscription costs.
I hope this clears things up!