Timetable clashes
You need to check the class hour and days for each module, as you cannot take modules which have a timetable clash. If the days are not specified you should assume there is a class at that time every day, Monday to Friday. Many modules involve compulsory tutorials, seminars, and labs as well as lectures, and you need to make sure these do not clash. There is often a choice of days for labs, to allow you to fit round commitments to other subjects.
Note that it is common for some module combinations not to be possible within a particular degree programme, due to timetabling constraints, particularly in joint programmes.
Classes last approximately 50 minutes unless otherwise stated, so there should be enough time for you to get between classes that start at consecutive hours. For example, it should be fine to take a module at 10am and another at 11am.