"localtime" and "ddx" do not work together in the same rule

deCONZ REST-API Support
1

In this example, why doesn’t “ddx” work with “localtime” ? I seem to recall seeing questions about this on GitHub.
Is there a technical reason why they don’t work together ?

{
    "actions": [
        {
            "address": "/sensors/1/state",
            "body": {
                "flag": false
            },
            "method": "PUT"
        }
    ],
    "conditions": [
        {
            "address": "/config/localtime",
            "operator": "in",
            "value": "T08:00:00/T20:00:00"
        },
        {
            "address": "/sensors/1/state/flag",
            "operator": "ddx",
            "value": "PT00:01:00"
        },
        {
            "address": "/sensors/1/state/flag",
            "operator": "eq",
            "value": "true"
        }
    ],
    "name": "rules_1"
}