I tend to just look on a periodic basis, might buy, or sell, at any time ... if the price is right. In effect look when I have the time to potentially follow that through with trade(s).
Coin/gold dealers spreads tend to range, if they have much gold on their books their sell/your buy price might move closer to spot, whilst their buy/your sell price moves deeper away from spot. At other times when they have low levels of gold and demand is rising they shift spreads the other way. For low churn/demand/supply items the spreads can be very wide.
Selectively bought and later sold at relatively good levels and there can be opportunities to have both bought and sold with in effect 0% dealer spread having been paid. Dealers don't want to be out-of-stock, nor have too much gold that's not moving.
Some weeks back for instance and the above dealer was buying Britannia one ounce gold coins at +1% above spot, along with having Out-of-Stock flags against their Britannia coin listings. At other times, maybe after the dealer having made a large purchase, they might have their sell price at 1% above spot, their buy price at 2% below spot (a.k.a they had enough already, didn't want to buy more, were looking to sell what they already had).
Holding liquid paper gold (gold ETF) facilitates keeping overall actual desired level of gold exposure aligned. So if for instance you hold $100K of gold ETF, $200K of physical gold, $300K total gold, but then buy $10K more worth of physical gold, align that with selling $10K of gold ETF ... and you still have $300K of combined/total gold.