VED session time limits

[jwjwjw]

I have a inexpensive VED that I bought from Amazon a couple of years ago and it works just fine.
A few days ago I was looking through the instruction booklet for this ved and it said that this ved should be used no more than 20 minutes.
I "think" this is considerably more than I have read about veds length of use on Frank talk.

Has anybody used ved's approaching 20 minutes continuously and did you have any issues doing that?