At the same time I am a little concerned based on some reading from various "experts" such as the following thinking from Schwab:

“We moved to a neutral view on emerging markets in November, concerned about high expectations and valuations. The addition of inflation worries and potential for lower capital inflows into these economies emboldens our conviction.

Broadly speaking, that view is not too far from our own that, at present, a good number of emerging markets stocks and ETFs are expensive relative to their risk/reward profiles. However, I don't think that precludes anyone from starting to increase their EM exposure today. The key, though, is to pay attention to the "Best Buy," "Buy," and "Hold" guidance on our recommendations page, steering clear of the "Holds" for the time being.

http://newsletters.fool.com/25/scorecard/index.aspx

In terms of timing, there is no great advice here. One could do it all at once, which shouldn't alter a portfolio's risk profile all that much provided you are just shifting between risk assets (not moving bonds to stocks, for example) and have a long time horizon on your risk assets, or you could commit to doing a little regularly. Whatever makes the investor most comfortable and less likely to be angry if something goes wrong is generally the right course in my experience.

Tim