Hi, Amazonas is a rough place, with amazing, marvelous natural settings, but tourist services are not well organized. Air or ground connections are not easy to get there. Just one flight a day, from Sunday through Fryday, usually delayed or canceled... a headache.
If flying from Caracas, it's easy to get Puerto Ordaz and head on the way to Canaima or Delta. The best plan consists in spending overnight in Puerto Ordaz before departing to Delta (you may contact Campamento Oridelta or Sacoroco River Tours) or spending overnight in Ciudad Bolívar before departing to Canaima (you may contact Excursiones Kavac o Posada Wey Tepuy). These are some tour operators I know and who I trust in.
3days-2nights packs are available in both Canaima and Delta; thus, you will have the chance to connect a flight to Caracas on the same day you are back from Canaima or Delta.
Commuting to Canaima: flights depart from Puerto Ordaz or Ciudad Bolívar at early morning. More choices and better prices in Ciudad Bolívar. Ground travel time between Ciudad Bolívar and Puerto Ordaz is 1 hour long or so.
Commuting to Delta: road tip from Puerto Ordaz to Delta camps is 90 minutes or so. In-and-out private transfer must be dealed.
Expect this information is ok for your travel planning.