Need to configure timer to execute on specific date and time in Start Event node of Process Model

As per other suggestions here, xor and a start node timer to run at intervals with a definitive end date seems to be the best way to achieve this! There was error in my earlier suggestion so try this way. 

Hi Harsha, Thanks for your response.

But now calculates seconds also. So output of

rule!ExpressionRuleName()=now() is never becoming true. If I apply rule!ExpressionRuleName()>=now() then it is becoming true but in that case it will become true next day onwards as well and I want to run this PM only once on that specific date and time.

I have updated the answer above to adjust this. Have a look

Running an expression inside a start node timer will not work. It evaluates that expression only once an the time of publish or deployment.

If you have to use this expression, start the process in a 10 minutes interval, and evaluate the current time against the expression output in an XOR. Then, either continue the process, or go to an end node.

Timer expressions are evaluated at specific intervals, not dynamically during runtime. The solution is to configure a periodic timer that triggers at regular intervals, then immediately add an XOR Gateway with the condition now() >= rule!YourExpressionRule(). When the condition matches, proceed with your workflow; otherwise, terminate the instance at an End node. This creates a polling mechanism that monitors at each interval until your specified datetime arrives.

Remember to set the process model to Inactive after your target datetime to stop recurring.