遅れなければ大丈夫のはずなのですが

あくまで同時に購入（乗り継ぎとして）場合。

多分、
1200 H Cebu 1320 H Manila
1520 H Manila 1955 H Osaka (Kansai)ですよね。

でも遅れたらおしまい。でも関西からセブまで買えるのに、何故わざわざ別々に？

Flight Connections
Cebu Pacific is a point-to-point carrier and will not be liable for any misconnections brought about by delays and cancellations.

Guest and baggage will be checked only up to the sector for which you
have checked in. Guests with connecting flights are required to claim
all baggage and clear through Immigration and Customs in all airports
and recheck-in to their connecting flight.

However, Cebu Pacific offers connections within Cebu Pacific’s network
and are sold as such. Only guests on these flight connections with a single fare
will be considered connecting guests and will be treated as such. Guests
who may have bought connecting flights but not under a single fare
(that is, build their own flights) will be treated on a per sector basis.

上記の通り、”a single fare”で購入した場合のみの話し。

恐らく、別別では荷物を再度預けることが必要です。また、遅れても一切補償なしです。