As an Excel novice I need some help! I have one sheet (let's call it sheet 1) with lots of columns (up to AO) and rows (454) in it. I am trying to get a cell in another sheet (sheet 2) in the same file to pull in and sum some of the data to create a summary. Sheets 1 and 2 share the same first two columns, an "ID" column (A) and "Name" column (B). ID cells contain a reference number. Name cells contain a place name. The cell entries in the ID column (A) are not all different - some share the same ID and also Name in the second column (B). I then have another column (C) which is titled "When". These cells contain a day and time of the week such as "Sat am", "Sun pm", Thurs pm", etc. I then have a fourth column (D) which is titled "How long". The cell entries contain figures in hours - it could be 3, 0.75, 0.5, 2.5, etc.

Basically, in sheet 2, I want to be able to create a summary which shows my column A data and column B data shown only once (remember there are multiple entries of the same A and B data in sheet 1) and then in the third column (C) I want to sum the figures from sheet 1 column D "How long" that relate to the column A ID and column B Name entries in sheet 1 but have only been identified in sheet 1 column C "When" as "Sat am", Sat pm", "Sun am" or "Sun pm".
I've been struggling trying to find a VLOOKUP or SUMIF formula that works but to know avail. Note that I have 454 rows of data - I have heard that VLOOKUP only works for 255 or thereabouts? Any steer much appreciated!