This is the second pre-release of MicroPython for SAMD21x18 boards including the Arduino Zero (available from Adafruit) and Adafruit Feather M0 Bluefruit LE.
It adds float support! So, time.sleep(0.5) works.
See here for flashing instructions.
adafruit/circuitpython
v1.8.3-61-g559434a
on GitHub
pre-release8 years ago