Lets have two different members of the feature vector to represent data. One will be a boolean indicating weekday or weekend. the other can be int taking on one of 4 values for morning, afternoon, evening and night. This will make the encoding simpler.

Also the java Data, Time and Calendar classes allow you to parse a well formatted data string (such as the one returned by twitter) into an object and then extract properties about the Date like day of week etc.

Take a look at this example (http://stackoverflow.com/questions/4637238/how-to-check-if-its-saturday-sunday) and lets try to make this more robust, rather that extracting substrings ourselves