They’re both really really close to perfect, and any native speaker would understand exactly what you’re saying with no problem, but I’d say them like this:
“I won’t be at my computer much today, I have to be somewhere.”
and
“It’s incredible how time flies! It will be Christmas soon!”
Yeah I still rely on fansubs for all my jdramas that don’t get official releases outside Japan (which is still most of them). The quality is instantly obvious compared to machine-generated crap.
Cultural context and an understanding of tone and narrative coherence is critical for subtitles if you want to do justice to the quality of the writing in the original language.