Tour Furano and Biei in one day?

Planning to check out lavender in Furano in July. I have never been to Biei - is it realistic to plan to see both Furano and Biei on the same day? How much time should I allocate for Biei until places close/sunset in July?

There is no limit for that. If you have no time, just drive along the road.

This site estimates 160 minutes from Asahikawa to Furano.
http://www.mapfan.com/kankou/special/hokkaido/drive.html

This site shows three patterns:
1: The shortest: 9:00 Asahikawa - 11:50 Asahikawa Airport
2: Recommended: 9:00 Asahikawa - 16:10 Farm Tomita
3: The best: 6:00 Asahikawa - 15:00 Shikisai No Oka
https://hokkaido-labo.com/furano-biei-2746

This site for lavenders in Furano. 1.5 - 2 hours for each lavender farm.
http://www.tabirai.net/sightseeing/tatsujin/0000243.aspx

Routes maps for the above.

1: The shortest: 9:00 Asahikawa - 11:50 Asahikawa Airport
https://www.google.com/maps/d/viewer?mid=19EOiLAX6GL1bDjGt80zvBTN7lqw&...

2: Recommended: 9:00 Asahikawa - 16:10 Farm Tomita
https://www.google.com/maps/d/viewer?mid=1f168vWprlPPjIWyXeDshpZTByeQ&...

3: The best: 6:00 Asahikawa - 15:00 Shikisai No Oka
https://www.google.com/maps/d/viewer?mid=1jMnJ8u_5AvnLQVCCqGfR9EjON8c&...