Predict datetime variable with orange canvas
It appears those numbers are Unix timestamps. The numbers you quote correspond to the following human-readable dates in ISO format:

Epoch date  Human readable date (GMT) 
1450396800  2015-12-18 00:00:00
1438905600  2015-08-07 00:00:00
1438732800  2015-08-05 00:00:00


You can use an online epoch converter to confirm.

Apparently, Predictions widget treats datetime variables as continuous variables (which is ok) but fails to present them nicely. You should probably submit a bug report about it.