First of all you shud use the Grade of engine oil spec'd by Volvo, which is 10W30.
Using 5W30 for "cold start protection" ???? where do you live? Near the Canadian border??? many days that are below 10deg F.
The Oil pressure light shud go out 1 to 3 seconds. One of the reasons it may take longer is that the Oil Filter has a failed or poorly working FlowBack valve. A bad valve lets the oil get sucked out of the filter after the engine is shut off, leaving the oil filter itself Low on Oil. When you start the engine again the oil pump must fill up the filter first. An easy check on this is to remove the filter after the engine has been off, say overnight.
If this proves to be the case, use another brand of Filter.
There are other reasons for the Oil Pressure light delay. But the first is usually the Filter.
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