See here for the programme structure and module timetable
In terms of timing, you will finish your module examinations in May of your second year, and will then have until December of the same year in which to complete your thesis. If you don't make this deadline but have made reasonable progress with your project, you will have be invited register for another semester and pay a further fee.
The marks breakdown follows the credit structure, so each specialised module contributes about 11% to your final grade.
UCD Student Regulations
The rules the University, including the Academic Regulations and Student Code are available here: http://www.ucd.ie/registry/academicsecretariat/regs_home.htm.
Final Grades
The overall possible MSc grades are: 1st honours, 2.1 honours, 2.2 honours and Pass. This document explains grade calculation and exam results.
Exit Routes
If you complete and pass all modules but fail to complete the main ASE project, you will be awarded a Graduate Diploma in Advanced Software Engineering. You may still return at a later date to complete the MSc under Recognised Prior Learning (RPL). The RPL would be general credit for the 60 credits of the Grad Dip, and so the MSc award would be calculated based on the 30 credit dissertation.