Let's Say 100 other users Time Locks are expiring at the same time as yours , and all drawing out at least $100.
Total amount is now 100users*$100=$10,000
Average # of transactions per block ~2000.
At $1 each , it cost me $2,000 bucks to spam the block locking out all of your transactions and including mine, that lets me steal the entire $10,000 .
So My Profit is $8,000 , not bad for less than 30 minutes worth of work.
They're going to have to fill more than 1 block. Unless they ALL try and cash out ON the block the time lock expires.. They won't..
Until segwit is activated, you have to trust them.
Until SegWit is activated - BTC ain't going nowhere.. and LN too.. so I'm assuming this all happens after that.