/help /echo

The -iN switch indents the wrapped line by N characters.

$indent return length of timestamp if timestamp is enabled.

If you make mIRC theme, can use:
echo -ti $+ $calc($indent + 5) -!- bla bla bla)..

alias indent {
  var %indent = 0
  if ($gettok($readini($mircini,options,n4),12,44)) var %indent = %indent + $len($timestamp)
  return %indent
}