I don't know about the loss of spouse, but the rule for divorce is it takes 2 years to get back to normal. I think that's a good estimate. Losses take time to heal.
However, when one becomes a senior citizen time becomes much more of an issue. The reality is if you are 65 and you want to find a partner for pickle-ball, dancing and travel you only have so many good years left. So, there is an incentive to find the right or nearly right person sooner than later.
In fact for many oldsters a FWB relationship fits the bill very nicely. Just make sure you agree ahead of time on what the benefits are.