You could enter time from the Employee Table via a portal. You could enter in a portal on Jobs Table. The time could be entered directly to the Time Table. What work flow makes the most sense for you. The record would need an identifier to summarize by Job. Entering from a portal would have that. You would need a drop down I think for Jobs to do it from other tables.
Part 2 describes a summary report. Here's a tutorial on them: Creating Filemaker Pro summary reports--Tutorial
Part 3: Can't tell from the data described. You can certainly add that link if you need to. It would allow you to show information from the Job table on the layout where you are logging the employee's hours. Whether that is useful to you or not is your call.