Believable or realistic?

[Moiinuae]

A question of opinions based on your experience:

We have received the offer of a 3-month engagement in a government agency. Terms seem good - ticket to/from home country, accommodations, good fee. THing is the guy wants an early Sept start which would be fine except of everything we're hearing about things taking forever.

Long story behind it (we know we need a contract, we know that nothing is serious until signed, and even then...etc etc) and we're waiting to hear back from this guy for a final go and don't even know if he's checked in with HR, but in the meantime we are biting our nails and wondering:

Has anyone ever been able to go on a 3-month consulting engagement with such short notice? If so, how does that work? I know about mission visa - but are there still requirements still like attestations, security, etc etc?

Our concern is that if this guy realizes it's absolutely impossible (been our assumption so far), then he'll start the project anyhow because he needs to get it done.

Thanks in advance for your thoughts.