Neat! We've been doing something like this at work, and another simple solution (curious if your Google cloud infrastructure is built on something similar) is Azure Service Bus queues with a function app trigger.

Unlike AWS SQS, Azure SB queues can have items scheduled to be queued at an arbitrary time, see https://docs.microsoft.com/en-us/dotnet/api/microsoft.azure..... SQS can only delay up to 15 minutes, so you have to implement your own hack to schedule for later than that.

And also unlike SQS, they can trigger a function so you don't have to deal with the logic to listen yourself - or even the transactional message handling, if the function fails the message is automatically re-queued.