I sometimes sit in my car for an hour after work so my boyfriend thinks I work later than I actually do

My boyfriend and I moved in together about six months ago and everything is genuinely fine between us. We dont fight much, he gives me space, and there isnt some horrible relationship problem I'm avoiding. But a couple months after moving in together I started doing this thing where I dont go home immediately after work. My shift usually ends around 5, but he thinks I finish closer to 6 because thats what my schedule used to be. I never corrected him. Most days I drive to a supermarket parking lot or somewhere quiet, buy a coffee, put my phone on do not disturb and just sit there for 40 minutes to an hour. Sometimes I listen to music. Sometimes I scroll on my phone. A few times I've literally just sat there doing absolutely nothing. I dont even know why I need it so much. I love coming home to him, but theres something about that little period where nobody knows where I am, nobody needs anything from me and I dont have to talk that feels ridiculously peaceful. The weird part is I've started protecting it like its an actual appointment. If he texts asking when I'll be home, I'll say “probably around 6:15” while I'm sitting five minutes away from our apartment. Last week he surprised me by making dinner early because he thought I had a shorter day. He called at 5:30 asking where I was and I lied without even thinking and said I was still finishing something at work. I felt like shit afterward because he sounded so sweet on the phone. I know this would probably be completely normal if I just told him I need an hour alone after work. For some reason though, saying “I need time before I come home to you” sounds so much worse than what it actually feels like in my head. So instead I've accidentally created this whole fake extra hour of employment just so I can sit alone in my car.