imo, the better your availability, the higher the likelihood of getting hired.

however, if you tell them off the bat that you want 40+ hours i think that hurts your application/interview because it comes off that you need the hours and are dependent on the job for income (whether this may be true or not). as retail shifts usually last around 6 hours (from my experience), it is unlikely that you will be able to work over 40 hours, unless you work 7 days a week.

for aritzia - i didn't have any work experience prior to applying there and got hired. so i definitely think you should go for it! good luck with your job search!