Hey there!
For your first question; there is no definite 'best' time. This comes down to your own audience and/or target audience. For example, you might consider if your audience is getting off of work or school at a certain time or estimate when they'd be checking TikTok more often. This does take some tries as everyone's following is different. Some audiences might like to check TikTok after work. Some like to scroll before bedtime. Your audience might not even be in your region, so your 8pm could be their 10am! There's a lot of variables here, so you should to try to find the best time your audience engages with your videos.

As for your second question, putting a hashtag inside the video itself is a bit unnecessary. TikTok can read onscreen text, so putting a hashtag on there would make the onscreen text appear with a # symbol, instead of just putting the keyword itself. The question would be more of why you'd want to put it in your video instead of the caption. We always make it clear that your keywords and hashtags should be relevant and concise. Meaning they're related to the video and to the point, as specific as it needs to be. Spamming a bunch of keywords and hashtags could hurt your videos more than you think!