If you're cycling off and on at 20~30 seconds I would not worry about it...this is fairly normal, especially at the temperatures you mention. Drive it and see how it does in the warm. I would not touch the high pressure side. Leave that for professionals....dangerous! Actually, the recommended fill temp is 60F or more, so you filled at lower temp, but like you said, there is a pressure release if too much gas is in there, so there really isn't any worry. Besides, the pressure in the cans (from what I understand) is not enough to over-load the A/C system (unless you're using a big metal tank), so whatever the Volvo A/C system is willing to take in from the cans will be fine (from what I understand).

I have to fill mine too. Last spring I filled mine as temp was not changing with A/C on or off in the cabin. I thought my Evap was bad but it wasn't. I'm hoping that winter cold shrunk the "O" rings and I lost coolant again. May get lucky with a fill, but my Evap for sure may be gone this time, but I hope not.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.