Question : Is there a funtion that if I use substr(col,1,1) will tell me where a value is not a character

I am trying to clean up data where I'm trying to read in numbers.  

These values are all in a text field and if it is a numeric value I use a to_number (substr(col,1,1) to convert it to a number.  If the value is other than a number and can't be converted it crashes.

 Is the a function I can put in the WHERE clause to skip non numeric values?  Like

WHERE   (substr(col,1,1) != ?

Answer : Is there a funtion that if I use substr(col,1,1) will tell me where a value is not a character

I believe, that you would divide 1 by the instruction clock, (in this case giving 250nS). therefore one instruction takes approx 250nS. then divide your required delay XmS by 250nS to give required number of instructions to complete the delay.
i.e for a 250mS delay you would require (0.250/0.00000025) 1 million instructions