Azure Function Durable Timer does not wake up until app is touched

Question

I have a Durable Orchestration that scales up and down Azure Cosmos DB throughput on request. The scale up is triggered via HTTP, and the scale down happens later via a Durable Timer that is supposed to wake up the Azure Function at the end of the current or next hour. Here is the Orchestrator Function:

public static class CosmosDbScalerOrchestrator
{
    [FunctionName(nameof(CosmosDbScalerOrchestrator))]
    public static async Task RunOrchestrator(
        [OrchestrationTrigger] IDurableOrchestrationContext context)
    {
        var cosmosDbScalerRequestString = context.GetInput<string>();

        var didScale = await context.CallActivityAsync<bool>(nameof(ScaleUpActivityTrigger), cosmosDbScalerRequestString);

        if (didScale)
        {
            var minutesUntilLastMinuteOfHour = 59 - context.CurrentUtcDateTime.Minute;
            var minutesUntilScaleDown = minutesUntilLastMinuteOfHour < 15
                ? minutesUntilLastMinuteOfHour + 60
                : minutesUntilLastMinuteOfHour;
            var timeUntilScaleDown = context.CurrentUtcDateTime.Add(TimeSpan.FromMinutes(minutesUntilScaleDown));
            await context.CreateTimer(timeUntilScaleDown, CancellationToken.None);
            await context.CallActivityAsync(nameof(ScaleDownActivityTrigger), cosmosDbScalerRequestString);
        }
    }
}

Here is the ScaleUpActivityTrigger:

public class ScaleUpActivityTrigger
{
    [FunctionName(nameof(ScaleUpActivityTrigger))]
    public static async Task<bool> Run([ActivityTrigger] string cosmosDbScalerRequestString, ILogger log)
    {
        var cosmosDbScalerRequest =
            StorageFramework.Storage.Deserialize<CosmosDbScalerRequest>(cosmosDbScalerRequestString);

        var scaler = new ContainerScaler(cosmosDbScalerRequest.ContainerId);
        var currentThroughputForContainer = await scaler.GetThroughputForContainer();

        // Return if would scale down
        if (currentThroughputForContainer > cosmosDbScalerRequest.RequestedThroughput) return false;

        var newThroughput = cosmosDbScalerRequest.RequestedThroughput < 25000
            ? cosmosDbScalerRequest.RequestedThroughput
            : 25000;
        await scaler.Scale(newThroughput);

        return true;
    }
}

and the ScaleDownActivityTrigger:

public class ScaleDownActivityTrigger
{
    [FunctionName(nameof(ScaleDownActivityTrigger))]
    public static async Task Run([ActivityTrigger] string cosmosDbScalerRequestString, ILogger log)
    {
        var cosmosDbScalerRequest =
            StorageFramework.Storage.Deserialize<CosmosDbScalerRequest>(cosmosDbScalerRequestString);
        var scaler = new ContainerScaler(cosmosDbScalerRequest.ContainerId);
        var minimumRusForContainer = await scaler.GetMinimumRusForContainer();
        await scaler.Scale(minimumRusForContainer);
    }
}

However, what I observe is that the Function is not awakened until something else triggers the Durable Orchestration. Notice the difference in the timestamps for when this was scheduled and when it happened.

Is the fact that it did not wake up until then by design, or a bug? If it is by design, how can I wake it up when I actually want to?