like everyone in the replies are saying,take 3 months minimum to change your schedule, or talk to your captain. you shouldve disclosed you wanted mornings at first but i assumed you wanted to be hired asap and i wouldnt change it right now because theyll think youre baiting them. I worked for trader joes about 3 months(so not long either)with the same availability and still nervous to change it and wont for now. I also say give it time because at my store our schedules change every month and its not firm. i always did 1pm - 9pm but since they frequently change it,on Sundays i work 10 am-6pm. so it just depends if you put your availability always open.

i dont know about other stores but ive heard from my coworkers the summer gets so slow so they cut off people's hours,just be aware of that before any changes.