Legal Question in Landlord & Tenant Law in California

Yup, if that is his actual cost.

Taking time off from work to do repairs is not a proper deduction from a security deposit. Civil Code section 1950.5 states that security deposits may only be used to (1) compensate the LL for defaults in rent, (2) repair damages not including wear and tear, and (3) cleaning. Loss of time or loss of earnings is not listed in statute as a proper deduction from a security deposit.

If the $300 refers to the cost of the repairs made over and above ordinary wear and tear, then that's legitimate. But in no instance can the LL compensate himself for time.

The measure of recoverable damages is the cost of doing the work on the unit, not what wages he failed to earn at his normal job. My limited experience has been that some judges will not allow the landlord to charge for his own time and only allow recovery for his out of pocket expenses; other judges require some proof as to what the labor should have cost, by requiring an estimate from some one who does that type of work for a living.