Typically, after targeting a key phrase that get's about 600 searches a day and getting good backlinks, how long would you estimate it would take to get in the top 10 or top 5 of a PR 0-1 dominated top 10?
Depends on the quantity and quality of the backlinks those PR0-1 sites have. PR doesn't say anything about SERP's. Also depends on your site's age and quality of links to your site.
Indeed. You shouldn't worry too much about when exactly this will happen, but focus more on creating quality content for your site. And if you are requesting link exchanges, dont forget to change the anchor text once in a while.
As you can see from previous responses there are too many variable to give you a definitive answer to your question. However, in general lower PR sites are crawled less frequently so if all things are equal(rarely) you could theoretically overtake those sites rather quickly(less than 30 days) if you get quality backlinks from high PR (PR5+)with content relevant to yours. If your competition has poor backlinks then even the relevancy issue is not as important in the short term as just getting the backlinks themselves. Good luck.