You're setting the norm that feedback runs in both directions from the start. Wait too long and asking starts to feel like an event instead of a habit.
If the first time your team gives you feedback is in month six, you've already lost three months of course-correcting. Asking early, before it's expected of you, sets the norm that this runs both ways from the start.
Step 1: Ask a specific question, not a general one
"How am I doing?" invites a polite non-answer. "What's one thing I could do differently in our 1:1s?" invites something usable.
Step 2: Offer a written option, not just a spoken one
Some people will tell you more in an anonymous form than in conversation this early in the relationship. Offer both channels.
Step 3: Respond to what you hear, visibly
Even a small, visible change based on feedback teaches people it was worth their time to give it. Silence after asking teaches the opposite.
Step 4: Ask again at day 180
One round isn't a habit, it's an event. Repeating it on a set schedule is what actually builds the norm.