Timbaland -- Time To Fess Up Over 'Stolen' Watch

Timbaland is a big fat liar who's trying to get one over on his insurance company by filing a bogus $1.8 million claim over a missing watch ... this according to legal docs filed by the insurance company.

TMZ broke the story ... Timbaland filed a lawsuit against American Home Assurance Company claiming his 2-year-old daughter lost his Jacob & Co. watch bedazzled with 30 carats of diamonds ... and the insurance company won't ante up.

But in new legal docs ... A.H.A.C. claims it doesn't owe Timbaland a dime -- claiming he's been as slippery as a seal, lying like a rug. The insurance company claims:

-- Timbaland bought the watch for $900,000 but insured it for TWICE the purchase price.

-- Timbaland reported the watch stolen ... but 4 months later claimed his daughter misplaced it.

-- Everyone involved told a different story ... the wife implicated another female, the assistant implicated the maid, the maid only copped to sleeping with Timbaland's brother-in-law and the brother-in-law refused to cooperate. No one ever mentioned the daughter losing the watch, like Timbaland belatedly claimed.