I find that the `if` statement here really makes it harder to understand the logic at first glance. I think a small refactoring to remove the use of the `if` improves readability and clarity. The way I would rewrite it would be like this:
```
generate_key(AddLeewayP) ->
    Now = os:timestamp(),
    list_to_binary([key_timestamp(Now, AddLeewayP), $_, key_suffix(Now)]).

key_timestamp(Time, true) ->
    timestamp(Time) + leeway_seconds();
key_timestamp(Time, false) ->
    timestamp(Time).

key_suffix(Time) ->
    random:seed(Time),
    integer_to_list(random:uniform(?GC_KEY_SUFFIX_MAX)).
```