I wouldn't worry about pushing him on the distance unless you actively want him to walk further with you. I understand the worry behind it - our dog's needs changed quite noticeably after being neutered in January and I still worry sometimes that we don't give him "enough"!
After scouring the internet (source of all truth, naturally) I've come down firmly on the side of "he has a wonderful time on his walks, he is sometimes keen to play if you offer him a game at lunchtime but sometimes can't be arsed, and he makes extremely contended groans regularly whilst settled during the day. He's fine".
He does make it quite obvious(!) when he would like something from you - varies from scratching at the back door, pawing at you, or (a favourite) shoving his paws in my book so I stop reading and pay him more attention. Obviously we're working on him being slightly more polite, but it does mean if I'm reading and he's snoozing on my feet I no longer worry that he's bored and not letting me know.
He gets a minimum of 45 mins off lead in the morning and 35 mins with some on lead, some long lead, some off lead in the afternoon. It's usually more like 50-55 mins and then 45mins though. Sometimes a run with me or a longer walk at a weekend, sometimes not.
He needed more before neutering (unsure if that was age/still settling in here after a traumatic previous home/the actual neutering itself) and he would be disruptive and/or find his own entertainment if it wasn't provided by us.
He's a 2yo adopted border collie, and I think he's the laziest collie we've come across but he's a very happy boy!