This is more of a workplace culture issue. It sounds like your lifestyle may not fit with what the company expects. Although you may be capable of meeting all of your objectives and accomplishing your tasks in a smaller time window, you still risk being looked down upon for not matching the expectations that the company culture has. Based on what you described, it sounds like many organizations in Sri Lanka have similar standards, too.
Negotiate other benefits
Just as some organizations that are unwilling to consider a higher salary are willing to negotiate other benefits (e.g. time-off), consider negotiating some extra leave or holiday time in exchange for a "yes" answer to extended hours. You could strike a balance between longer standard hours but more time out of the office.
You didn't specify how often this problem arises or how many organizations you've found that have similar expectations, but you might be surprised to find that even where standards are relatively homogenous there are always exceptions. Perhaps you should keep searching with the goal of finding a good company culture fit more in line with your lifestyle goals.
How open are you to moving cities? Is there somewhere nearby that you can broaden your search to include? (Think 2-3 hours away, or whatever you're willing to consider.) It's a lot to sacrifice sometimes, and often more than it's worth, but worth considering. Of course, factor other differences in like salary and benefits.
Contract or freelance
Based on your experience or portfolio, perhaps you can find a role where your pay is based not on your hours committed but on your outcomes and performance. You might consider a self-employed operation or contract with the company on a project basis, which could reduce some of the man-hour expectations they may have.
Like @Pete answered, you're in a catch-22 here. I can't condone a "yes" answer where you really aren't prepared to deliver. It sets both you and your employer up for eventual disaster. You can't ethically promise something you can't make good on, and you risk suffering from burnout, relationship/marital problems, or unsustainable work/life balance.
Get creative and be sure to consider all your options!