In DAS, you will see a "S" o the montage (this is explained on Class 1 / Onboarding session)
The price is shown in the L1, L2 in the montage and in the chart (candlesticks) (this is explained on Class 1 / Onboarding session) The limit is your buying power, in case of high volatile stocks, the margin is reduced or non existent, this depend on your broker
In DAS about one second using marketable limit orders
In day trading we cover our shorts in the same day. If you swing trade, when short you would pay interest on the position size for each day you hold it overnight.