The only thing that can be said with certainty is that it is always a good time to get rid of your poor funds and switch to better funds, they will make up your losses faster. By switching you are not injecting new money but only making your poorly performing investment move to a better investment tool. There is no reason not to do this at the earliest except in cases when you will have to reap huge losses to exit the poor fund, you may wait for a certain time in such case and exit when the loss becomes tolerable to your mind.
There is one more certain thing, it is always a good time to invest in your long term goals. For a long term goal like 8-10 years away, the timing for dips is pointless, look at the nifty chart for ten years and you will see that the largest dip is also wiped out in no time and the market continues its uptrend. Yes, it can hurt more when it falls and you might even miss that extra buck but waiting for the big dip is an impossible task, it is just impossible to predict -- that is like the market, it is not about your intelligence.
And there is one more thing if I may say, purchase or 'invest' new money when the market is going up, it could be the rock bottom and the start of a new bull market or it could be the middle of a bull market, but invest in a bull market. Do not invest when the markets are tumbling down.