Tethering Puppy - 7 Months Old

Hi everyone! Got a golden mix (may be with lab may be with great pyr, getting a DNA test soon) about 2.5 weeks ago, he's estimated to be about 7 months old. He is good in his crate and we do enforced naps through the day (2-3 depending on the day). We play with him and then take him on two good walks a day (20/30 mins) outside of quick potty breaks. We try and get him to settle on his own and sometimes its successful but in the times that he doesn't (and gets bitey/jumpy) we do go to tethering him in a space with his bed and will do a long lasting chew or bone.

My question is - how much tethering is too much tethering? We want to have him learn how to settle on his own eventually. When he does tether he settles pretty quickly while we're sitting at the table/on the couch. Also - should we be exercising him more? We're bringing in a private dog trainer on Tuesday for some of these questions but just curious if we're doing too much tether time. TIA!