All enzymes used in Megazyme kits have been subject to extensive stability studies and not affected by short term ambient shipping and are of high stability in the form which they are supplied.
Megazyme ships hundreds of kits at ambient temperature without any issues however as soon as the kits are received the individual components should be stored as stated on the individual bottles / vials.
Most Megazyme kits are supplied with a standard reference analyte (e.g. the acetic acid kit K-ACET contains an acetic acid standard in bottle 5). You can assess the performance of the kit by testing the supplied standard and should expect that the reaction is complete in the time stated in the kit data-booket and that the expected value for the standard analyte is obtained within the experimental error allowed.