‘ ... for a period before and during ... ’

Hello, everyone,

“Pre-emption means that a strategy is designed to prevent a rival from starting some particular activity. In some case a pre-emptive move may simply be an announcement of some intent that might discourage rivals from doing the same. The idea of pre-emption implies that timing is sometimes very important — a decision or an action at one point in time might be much more rewarding than doing it at a different time point. Pre-emption may involve up-weighting advertising for a period before and during when a new entrant launches into a market. The intent is to make it more difficult for the new entrant’s advertising to make an impression on potential buyers. Product proliferation is another potential pre-emption strategy. The general idea is to launch a large variety of product variants so that there is very little in the way of market demand that are not accommodated. Arguably, if a market is already filled with product variants it is more difficult for competitors to find untapped pockets of market demand.”

1. While I think the ‘when’ in the underlined part above should be replaced with ‘which’ because the preceding noun is ’a period’, is my guess plausible?

2. Alternatively, is there a possibility that ‘the time’ has been left out as in “ ... for a period before and during (the time) when a new entrant ...“?

I would appreciate your valuable opinions.

* source; ‘Marketing Planning & Strategy: A Practical Introduction’