The periodic task that Bernie recommends is best as it takes advantage of the superior capabilities of the CLX platform. Learning to properly use tasks will improve your control and your programs.
If you are trying to maintain some semblance of compatibility with an existing ML program and you really do need a free running clock like the ML S:4 then it is simple enough to make one. Create an unconditional timer and call it S4 or whatever name suits you with a preset of 214783647 and unconditionally unlatch S4.acc.30.
S4.acc.30
---------+TON-------------+-(EN}---------(U)--
|Timer S4 +-(DN) *
|Preset 214783647|
|Accum 0|
+----------------+
*you can put output instructions in series in a CLX
Unlatching S4.acc.30 will guarantee that the timer will never time out.
S4.acc.0 has a period of 2mS
S4.acc.1 has a period of 4ms
S4.acc.2 has a period of 8mS
.
.
S4.acc.8 has a period of .512S
S4.acc.9 has a period of 1.024S
etc.
You will have available S4.acc.0 through S4.acc.29. You can assign an alias to any bit in S4.acc. For example, Rapid_Flash might alias S4.acc.8 and Slow_Flash might alias S4.acc.10