for CRS you don't need to stay 180 days, because you are considere a UAE resident from banks as long as your visa is valid, and your visa becomes invalid only if you stay more than 180 days outside of the country. So CRS is not an issue, if you set up things properly, basically you open a bank account with your emirates ID and a brokerage account with an EJARI as a proof of residence. NO CRS messages will be sent.
180 days is the required amount of time you have to spend in the UAE to get a tax
certificate and be almost sure to have no problem whatsoever with your country and with your money. It means that you have "paid" taxes on your money and if your home country has a double taxation avoidance agreement with the UAE they can't claim taxes on that money. It also makes the money spendable, because you now have a document which clarifies the source of the funds, which is something that is required in most countries when you buy a house. Remember that regulations varies by country, in Italy if you have a wife which resides in Italy, you are considered an italian resident and will ignore even a tax
certificate from Dubai because you have ties to the country.
So if you need or don't need the tax
certificate depends a lot on what you want to do.