Collect message till particular point of Time in BPM

Hi,

I want to collect messages till particular point in time like till 6 oclock evening.

In deadline branch i have to use Expression and should give date and time.

What is the format of date and time if it is not coming in payload.

What is the difference between: Creating the step and Creating the process property.

Any help is apreciated.

Thanks and regards,

Satish