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Hate to say this, but it depends. There are numerous factors that impact this. First AO in 3par is a scheduled task. You determine when to run it and what period of time to look at data to determine what moves. For example, we consider our business day to be 7am to 7pm. So we run AO in the evening with parameters that looks at usage from 7am to 7pm. This allows us to not have any maintenance jobs that run on systems over night to cause data to artificially raise up to higher tiers. Some might argue that if that maintenance job would benefit form higher tier it should move up, but our highest tier is space constrained.
Once AO run it will begin moving the data it feels needs to move to a given tier based on the parameters you supply. You can tell an AO configuration to skew its algorithm based on Performance, Balanced or Cost which basically means skew more data to Tier 0, evenly tier data or tier more to lowest tier. You also tell the AO task how long it can run, so that you can prevent it from running into your business day. We allow it to run 9 hours. So basically it depends how much data has to be moved and if it can move it all in the allotted time. For us once things normalize we have no problem in that AO runs well within its allotted time. If there are large changes in data, such as 10's of TBs of new storage provisioned then it may take days for thinsg to normalize again.
I know other arrays look at data usage every few minutes and move blocks, I can see the advantages and disadvantages of this approach as well as the 3par approach. Personally I don't know much about EMC, but I feel 3par slots in between EMC's VNX and VMAX lines.
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