How can a contractor's on-time record be checked?
Ask for references from comparable completed jobs and call them. Ask what the contract period was, when practical completion was certified, and how many variations were claimed. For larger public jobs, Singapore's Price-Quality Method scores past timeliness. For private work, look at the contractor's BCA registration and licences, and ask for a sample programme from a previous job.
From the RRD Field Guide, checked against the sources cited in Cheapest Quote vs Delay Risk: The Economics of Choosing a Contractor in Singapore. General information, not advice for your project.
The fuller picture
The cheapest quote is only cheaper if the job finishes on time and on scope. Overrun research shows delays are common and fat-tailed, so a small price saving can be wiped out by a few weeks of rent, lost revenue or holding-over. Compare quotes on expected total cost, including probability-weighted delay cost and the worst plausible outcome, not the tender price alone.