combine SQL queries

I have multiple queries to get data marked under different categories, with it returning the last X rows from before a given datetime. The max timestamp value will be different for each of the categories

SELECT * FROM table WHERE category="a" AND timestampCol < timestampValue1 ORDER BY timestampCol DESC LIMIT 3;
SELECT * FROM table WHERE category="b" AND timestampCol < timestampValue2 ORDER BY timestampCol DESC LIMIT 3;
SELECT * FROM table WHERE category="c" AND timestampCol < timestampValue3 ORDER BY timestampCol DESC LIMIT 3;
...

I would like to optimise this to run as a single query as it can be pulling from up to 8 categories at a time which is a lot of queries to be running.

I need the database to return a set number from each category. It would be nice to customize the LIMIT per category however this is not essential as long as I am guaranteed to have data return from all the categories.

I tried the query below, which will return the first 9 rows. But they could all be from category A, which is not what I want.

SELECT * FROM table WHERE
 (category="a" AND timestampCol < timestampValue1)
 OR (category="b" AND timestampCol < timestampValue2)
 OR (category="c" AND timestampCol < timestampValue3)
ORDER BY timestampCol DESC LIMIT 9;
...

Using GROUP BY on category would only return me one of each category instead of 3, unless there is a nice way I can get that to work?

How can I do this?

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