What format do I use to send date and time as a data type into Heap?

Time must be sent in ISO8601 data format to be readable by humans and usable as dates in Heap. You can set up the definition with filters like this:

While we do not currently support a Date data type for custom properties, our query engine converts these ISO8601 timestamps to unix milliseconds timestamps, and so can be used with greater than and less than operators to define time ranges, for example, in a Segment.