Simply put, they are performing more due diligence, reducing valuations and demanding earlier profitability through more controlled spending. With public markets so depressed some Angels are placing funds back into undervalued stocks at the expense of the early stage market. These are the key things required. The return on investment is obviously critical to a deal. This is a very hard question to answer, because every angel is different and every deal is different, but I will try.
Passive angels tend to invest in more deals at a time and usually want a quicker return.
Probably 12-24 months, cash or liquid paper. Active angels get involved in operating the business and quite often draw an income from the business if it can afford to pay. Both types of investor would accept shares in an acquiring company if they felt these were of a higher quality than the one they currently hold. Sometimes no due diligence is done if the investor knows you well or has invested in you before, but this rare and risky. Beyond that there are so many issues I would prefer to provide a more detail answer when I have access to my reference materials.