You should be able to use a python datetime as input type: https://docs.flyte.org/projects/cookbook/en/latest/auto/core/type_system/flyte_python_types.html Also the actual processing needs to be done inside a task. Workflows are basically a DSL to compose tasks. I.e. something like this (not tested):

from datetime import datetime
@task
def t(date: datetime = datetime(2022,1,1)):
    date = np.datetime64(date)
    ...

@workflows
def wf(date: datetime):
    t(date=date)