You can stay in the UK for up to 6 months.
You can also apply to change (‘switch’) to a Tier 1 Entrepreneur visa anytime within 6 months.
Tier 1 Entrepreneur visa: This Visa allows you to stay there for 3 years and 4 months. What you can and can’t do in UK…You can:
Go to meetings, conferences, interviews or site visits
Go to trade fairs, as long as they’re only for promoting your business and don’t involve selling anything directly to the public
Arrange deals, trade agreements or contracts
Speak at a one-off, not-for-profit conference
Check details of products and buy them
Recruit staff, as long as it’s for the business allowed by your visa

live in the UK for extended periods in the same category
work, including selling merchandise
get public funds
study
marry or register a civil partnership, or give notice of marriage or civil partnership
get private medical treatment
extend your visa into same category or switch into another category except tier 1 Entrepreneur
bring in family members (‘dependents’) – they must apply separately