You don’t have even an hour for your swim? You’re desperate to work out anyway? Great! If you have 30 minutes – use it for quick swim!
250m F/C @50%
200m F/C legs only
4x50m- 25m 100%sprint, 25m F/C @45% /15secs rest
250m F/C @40-50%
That gives you 900m of nice quick swim. Work your speed out. You should feel tired after!
Remember, lack of time is not an excuse!