Ideally, you should aim at submitting your visa application at least 1 month before the date of your scheduled trip to Belgium.
It is best to apply for a visa at least 3 weeks in advance, and not more than 3 months before the date of travel, to prevent any risks. Since individuals who travel to do business in Belgium typically have multiple trips to the country, the subsequent applications will be processed quicker after the first application.
Your visa extension application will most probably be rejected under normal circumstances. Your application could, however, be granted in some situations, such as late admission, humanitarian reasons, unforeseeable circumstances in your home country and essential personal and medical reasons. You may apply to the visa issuing authority in Belgium to apply for an extension. You’ll have to stay in the country while it is being processed.