before one knows it vs soon

before one knows it

• rapidly (and sometimes unexpectedly) 

soon

• Readily; willingly; used with would, or some other word expressing will. 

• Within a short time; quickly. 

• Early. 

• Short in length of time from the present. 

• Used as an alternative to express 'to be going to' in the form 'to be soon to' 

• early