Yeah I'd also likely chalk that up to their emotional state. Piccolo even confused the time thing with the RoSaT, thinking things there would occur at a way higher pacing. Gotenks was most of the time within the RoSaT and when they were unfused as base Goten and Trunks before, I think the stress of seeing the new Super Boo may have clouded their abilities to assess it straightout. When Super Boo broke the hourglass, it was right after Gohan had powered up firstly upon being enraged the ritual was taking too long/Elder Kaioshin seemed to be mocking the entire thing, right? Iirc the scene constructions coincided, though I may be mistaken, so I think Piccolo (while the kids were in the RoSaT already) was too stressed with Boo there and didn't notice it.
They only sensed Gohan when he was flying right towards them in a close range already as well haha, despite Piccolo noticing the chi approaching was huge. I think in-universe, their chi sensing was partially blocked due to how tense they were.