To get the response data you do need to indicate an RT in the time column for each tone. To get the fixed duration between each tone, you can use a minmax value for the trial that indicates the length of the fixed time. e.g., for a 2000ms interval, use a minmax value of 0-2000!

To ensure that the full 2000 ms are used, add the keyword "full" to your RT request like this:

RT:57,full

The result of all this is that DirectRT will continue automatically to the next tone after 2000ms and will not continue until that time occurs--even if the RT comes in before that.