18 months is, by precedent, the limit on contempt for refusal to decrypt[0], but this administration is happy to disregard any precedent that does not agree with them.

[0] https://arstechnica.com/tech-policy/2020/02/man-who-refused-...

Actually no, they are required to allow you to enter the country, but they will make it a hassle, to the point of dehydrating you and/or refusing bathroom access, and confiscate the device in the end and access is through other technical means.