I like hold always eth with I'm a big fan of this, real thinking i am a small holder and eth more time give me profits. Basically we know this is best currency and top number two rank with larger marketing investors. Almost some days boom and i hope after some days later i can decided sold.
Selling does not have a specific time. It spends on the market trend. The market right over uptrend for more than two days and within a few hours there can be a sharp fall.
It is most times better to invest in BTC to limit your loss, but with ore reduced profit, if what you are buying is not much, however, the reverse is the case if it is ethereum. With many funds, you should be able to invest in BTC with better returns or better still share it on both.
Selling has to be done at the right timing, that is correct especially if you are investing for short term only, but for long term investors, they'll need to find the good timing based on their target as well, that would mean it could take a long time if the market is not bullish.