To calculate the time elapsed from the start of the call until the bot reaches a specific block, you can use BPL expressions for working with dates and times. Each of these expressions is described in detail in the article: Date and time functions.
{utcNow}. This variable will store the start time of the conversation.$call_duration = dt.sub(@utcNow, $start_time)
The variable {call_duration} will store the time in seconds that has elapsed since the start of the call.