Yes, it takes a bit of time to give the right readings. It calibrates over an hour or so.
When a new sensor starts, it’s likely to give you exaggerated readings of high glucose levels. It takes around 24 hours to warm up and settle. There’s a filament under your skin that uses enzymes to attract glucose. The process takes a little time. Don’t worry about high readings in the first couple of hours after you fit a sensor.