Not all Bootstrap templates will work with Sitecake out of the box. Especially if templates have a lot of layers stacked with different z-index for elements. Such templates need to be adapted for Sitecake.
If the template is simple it requires just a couple of minutes to adapt.
If the template is complex, a lot of moving bells and whistles, layers and complexity, then it’s from a couple of hours to a couple of days.
BTW I see a lot of templates on template markets these days that are overloaded with CSS/JS animations that distract the user, make pages unusable on mobile and bring no value. Same animations, transitions and gimmicks from flash websites from 10 years ago are live again. People are using CSS animations just because they can.
We have front end developers in our network who can do template adaptation for $10-$20 per page. Just FYI.