There isn't a word limit - you can type as much as you want within the time limit.

I typically write 4 paragraphs:

1) intro, with thesis, acknowledgement of complexity of the issue, and an introduction of the examples I plan to discuss to support my thesis; usually 4 sentences

2) first (and best*) example; usually 4-5 sentences
-- for arg essay: discuss the flaw and how the flaw might be made better
-- for issue essay: explain example and discuss how this supports my thesis

3) second (and second-best) example
-- (same as paragraph 2)

4) conclusion, re-stating thesis and re-acknowledging complexity of issue, then wrapping up (basically summarizing how my examples supported my thesis); usually 4 sentences

* Note: many of us were taught in school to put the best example last. Don't do that here. If you find yourself low on time, the paragraph that will need to get cut down is paragraph 3 - and you don't want to rush through or minimize your best example. If necessary, it's better to do that with your 2nd best example.

Also, I listed the most common number of sentences per paragraph. These are complex sentences - average length 15-20 words. (Though it's a great idea to mix things up - have one very short sentence when you want to make a strong point; have a semi-colon sentence to show you know how to use complex structures; etc.)