user115606: Ignoring the economic reasons as to why this may or may not happen.  If for some reason the network hashrate suddenly dropped by 30% immediately after a difficulty adjustment and remained at that level until the next difficulty adjustment, how long would each block be expected to take to mine until the next difficulty adjustment.

user5406: You're trying to do 100% of the work with 70% of the workforce.
The expected block interval is to the target interval of 10 minutes as the total work is to the workforce:

Texp = 10 minutes  × (100% ÷ 70%) = 14.3 minutes

The difficulty reset would get extended by the same factor:

Dreset = 14 days × 100 ÷ 70  = 20 days

The expected block interval would be about 14.3 minutes for twenty days.

115606: <p>Ignoring the economic reasons as to why this may or may not happen.  If for some reason the network hashrate suddenly dropped by 30% immediately after a difficulty adjustment and remained at that level until the next difficulty adjustment, how long would each block be expected to take to mine until the next difficulty adjustment.</p>
 5406: <p>You're trying to do 100% of the work with 70% of the workforce.</p>
<p>The expected block interval is to the target interval of 10 minutes as the total work is to the workforce:</p>
<blockquote>
<p>T<sub>exp</sub> = 10 minutes  × (100% ÷ 70%) = 14.3 minutes</p>
</blockquote>
<p>The difficulty reset would get extended by the same factor:</p>
<blockquote>
<p>D<sub>reset</sub> = 14 days × 100 ÷ 70  = 20 days</p>
</blockquote>
<p>The expected block interval would be about 14.3 minutes for twenty days.</p>
