Based on the accepted answer of that Q, that XP is regular XP that you may spend whenever you wish (though your ST may require you to spend it at character creation, obviously.)
Witness the use of "may" instead of "may only/must/should/can only/etc":
For more experienced characters, the Storyteller might choose to award
Experience Points that may be spent before play begins.
Disallowing spending the XP later, which is otherwise a valid character building option (saving your XP for more costly improvements), would unbalance the game, which is not likely to be intended either by the designers or the ST. Nonetheless, again, consult your ST (or make up your mind about the issue, taking the above into consideration, if you're the ST. :))