Context :

Aims : We study the association between Giant Molecular Clouds ( GMCs ) and Young Stellar Cluster Candidates ( YSCCs ) , to shed light on the time evolution of local star formation episodes in the nearby galaxy M33 .

Methods : The CO ( J=2-1 ) IRAM-all-disk survey was used to identify and classify 566 GMCs with masses between 2 \times 10 ^ { 4 } and 2 \times 10 ^ { 6 } M _ { \odot } across the whole star forming disk of M33 .
In the same area , there are 630 YSCCs , identified using Spitzer-24 \mu m data .
Some YSCCs are embedded star-forming sites while the majority have GALEX-UV and H \alpha counterparts with estimated cluster masses and ages .

Results : The GMC classes correspond to different cloud evolutionary stages : inactive clouds are 32 \% of the total , classified clouds with embedded and exposed star formation are 16 \% and 52 \% of the total respectively .
Across the regular southern spiral arm , inactive clouds are preferentially located in the inner part of the arm , possibly suggesting a triggering of star formation as the cloud crosses the arm .
The spatial correlation between YSCCs and GMCs is extremely strong , with a typical separation of 17 pc , less than half the CO ( 2–1 ) beamsize , illustrating the remarkable physical link between the two populations .
GMCs and YSCCs follow the HI filaments , except in the outermost regions where the survey finds fewer GMCs than YSCCs likely due to undetected , low CO-luminosity clouds .
The distribution of the non-embedded YSCC ages peaks around 5 Myrs with only a few being as old as 8–10 Myrs .
These age estimates together with the number of GMCs in the various evolutionary stages lead us to conclude that 14 Myrs is a typical lifetime of a GMC in M33 , prior to cloud dispersal .
The inactive and embedded phases are short , lasting about 4 and 2 Myrs respectively .
This underlines that embedded YSCCs rapidly break out from the clouds and become partially visible in H \alpha or UV long before cloud dispersal .

Conclusions :