#### 7.2.124 time-interests

`(time-interests deltatime initial prefix [suffix])`
  Indicates that all interest-related messages, when separated by at least `deltatime` seconds of real time, should be preceded by the string `prefix` and followed by `suffix`; the first message is preceded by `initial`. All three are printf format strings, whose argument is the current clock time (in seconds) on that stream. A `deltatime` of zero timestamps every message. Typical usage:
  (time-interests .1 `(set-clock %g)` `(sleep-until %g)`) or
  (time-interests .1 `(set-clock %g)` "(sleep-until %g) (progn (set-clock %g)" ")") or
  (time-interests .1 "(set-clock %g)" "(if (> 0 (sleep-until %g)) (" "))".