VLOOKUP: Auto-complete a column (48 cells long) from a dropdown box

Hi everyone

Apologies in advance, I'm certain someone as already answered this question. I'm trying to create a timesheet. I'll describe what it needs briefly - the first column will be a list of times (10 minute blocks), 48 cells in total (for 8 hours). Column 2 will be blank, so the user can enter "Client Name", column 3 a dropdown list called "Activity" for the user to choose from.

We have 3 different start times; 8:00am, 8:30am and 9:00am. I am wanting to make a drop down box of these start times (For example, in A2), and when a time is selected (eg 8:00am), cells A3, A4 etc will auto complete from there (8:10am, 8:20am).

I've tried using VLOOKUP with a separate sheet holding the 3 columns of different start times, but I just can't seem to wrap my head around it and I'm quite stuck.

I work with people who are extremely computer illiterate, so I'm trying to make the process of recording time in our office as easy as possible! Any help at all would be greatly appreciated!