They don't ask for a "return ticket" in the UK. They ask for proof of leaving the Country within 90 days and that's because the visa only gives you 90 days in the Country, you need to meet the requirements of an 'extention of stay' if you want to stay longer than 90 days.
No length of time, just proof of an address, although it should be in the province where you open the account. Then you can bounce around. Just be aware to do some things bank related you have to return to the province/branch where you opened the account