Rob Kardashian & Blac Chyna: Time IS Money for Us ... $275k to Be Exact!!

Rob Kardashian and Blac Chyna clearly aren't sweating childcare expenses ... not based on the lavish timepieces they just purchased.

A source tells TMZ the newly-engaged couple met with celebrity jeweler Nick Bhindi to pick out his ... and hers Rolexes. Rob opted for a gold GMT Master 2, which is no longer in production, meaning it's worth a bunch. Chyna walked away with 2 rose gold watches.

We're told Rob's was the priciest at around $150,000, and Chyna's diamond-encrusted Rolie was $90k. Her diamond-free one was a far more reasonable $35k.