If you bought the time share for personal use, then just as in the case of a sale of a principal residence, no loss is allowed. If you bought the time share for investment purposes, you may be able to take the loss as a long-term capital loss.
Depreciation methods that allow faster write-offs than straight-line rates in the earlier periods of the useful life of an asset. For example, in the first few years of recovery, MACRS allows a 200% double declining balance write-off, twice the straight-line rate.