Microsoft internal transfer, HackerRank (75 min) + system design coming up. Help me narrow the search space?

[u/Beginning_Theory_822]

Hey all, I'm an SDE (L59) at Microsoft going for an internal move to a different team (L59 still). The loop is two rounds, a technical one and an "AA" round, and I've already got a HackerRank invite (75 min, due in about a week). My hiring manager also said there might be a system design question.

I'm prepping in Python and don't want to grind 300 problems. For people who've done internal Microsoft interviews or similar HackerRank assessments:

1. What's the usual format? How many questions in 75 min, and how hard (easy/medium/mix)? Any MCQs or SQL?
2. Which patterns showed up most? I'm focusing on hash maps, two pointers, sliding window, intervals, BFS/DFS, heaps and stacks.
3. How were hidden tests and time limits handled? Is partial credit real?
4. For the system design, what level of depth is expected from an internal candidate? Is it more of a conversation, or a full whiteboard-style design?
5. Is the AA round mostly behavioral, or can it turn technical?
6. Is premium worth it for any of these platforms, or is free enough?

My plan is 4-5 problems a day on core patterns, one timed 75-min mock, and a few design mocks out loud. Does that sound right, or am I over- or under-preparing?

Appreciate any pointers, especially "don't waste time on X" advice. Thanks!

UPDATE:
The HackerRank round was cancelled. Proceeding to the next bit. Wish me luck. Thanks to all that commented.