About interp_from_grid function

i want to extract multipoint,and then,extract specify hour of everyday,
for example, the Surface solar radiation downwards in era5-land is accumulations parameter,
I want to select 00:00 everyday as daily solar radiation . But after I use the ct.observation.interp_from_grid function,
the datetime index change to timestamp index, use cdstoolbox.cube.select can not extract by specify time,
I remember the previous version can do it,I think the latest update change it,Is there any other way to do it?

dewpoint_tem = ct.observation.interp_from_grid(dewpoint_tem, lon=lon, lat=lat)
tdew_thisyear = ct.cube.select(dewpoint_tem, start_time='2020-01-01')