Is there any minimum length of employment for a UK visitor visa application? Would it be risky to apply for the visa just after getting a job even if I have a satisfactory bank account?
There is no minimum length of employment (nor for that matter, that an individual be employed). Applicants are asked to demonstrate eligibility in the visa category requested and to provide a lot of background information: employment history, educational background, financial viability, family, connections to home country, etc.. Along with your premise for entering the UK, the ECO would use everything you present to come to a decision whether intentions are genuine and a visa issued.