Current pediatric psych RN here. Although it's not what they taught you in nursing school, realistically, it's good practice and time management, esp. if you have a hectic day with admissions and discharges. As long as you check your orders and follow the rights of med administration, you should be fine. Once you get the hang of administering psych meds and you've had the same patients for a while, you'll already anticipate what you're going to give, at what time, and to who and what to watch for (e.g. cheeking, first dose rxn, EPS, etc.) I like prepping all my meds before they're due in little cups, writing initials on each cup, and ordering them in accordance with my patent list. So for you, you can start prepping around 7, administer at 8 to until 10 to finish.
As for your preceptor, he/she needs to chill tf out. There's no need to "chew" anyone out, esp. when you're on orientation LEARNING the ways there... Dumb*ss preceptor. Apologies in advance if you end up liking and becoming best friends with your preceptor. I just can't stand some of the unnecessary harshness during orientation when you're just trying to learn.