I have an appointment for shadowing at a position where they want to hire someone ASAP, but I'm training at a new job and need an excuse for missing about 3 hours

I know this is probably shitty of me, I already feel bad. But I would still like some help.

I'm really hoping to land this job I have to shadow for. This will be my third time speaking with someone at the company. I did a phone interview, in person interview, and now they want me to shadow and I assume the team manager will also want to ask me some questions.

That said, I recently accepted a new job. It's fine, but I don't feel like it's the right fit for me. Honestly, I was broke and about to hit $0 in my bank so I accepted the job, because at the time, no one was calling me. I had to schedule the first 2 interviews pretty close to the date I started training. By the time they asked me to shadow, I had already begun training at my new job. I don't want to lose the job, in case I don't get hired by the new company, but this current job is really not what I'm looking for.

I feel like I need a good excuse, but I can't exactly say what I'm doing. I doubt, considering I'm training, that taking a personal day would be an acceptable excuse.

What can I say that sounds like a legit reason for me to be missing 3 hrs of the day?

TL;DR is basically in the title.

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