You dont have to inject anything to Cron plus .. the opposite ..
as @mickym2 said configure Cron plus (solar events) to inject and set a flow context variable that defines whether its day or night (a variable that can be later used in other parts of your flow to block execution)
For Example:
[{"id":"f58f72032eb7bd50","type":"cronplus","z":"54efb553244c241f","name":"","outputField":"payload","timeZone":"","persistDynamic":false,"commandResponseMsgOutput":"output1","outputs":1,"options":[{"name":"day","topic":"day","payloadType":"bool","payload":"true","expressionType":"solar","expression":"0 * * * * * *","location":"35.36038458458532 32.87109375","offset":"0","solarType":"selected","solarEvents":"sunrise"},{"name":"night","topic":"night","payloadType":"bool","payload":"false","expressionType":"solar","expression":"0 * * * * * *","location":"34.9291775968022 33.046875","offset":"0","solarType":"selected","solarEvents":"sunset"}],"x":540,"y":1260,"wires":[["b3f1ab45e814b0b8"]]},{"id":"b3f1ab45e814b0b8","type":"change","z":"54efb553244c241f","name":"","rules":[{"t":"set","p":"isDay","pt":"flow","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":720,"y":1260,"wires":[[]]}]
If its day .. flow.isDay
will be true
if its night .. flow.isDay
will false