Fourtrak's tend to do this, the power needed to energise the starter solonoid has literally to build up to the point where it engages the starter pinion. This is a trait, if it always starts first time, the starter is working, and it is not struggling simply live with it.

If this is causing a problem strip the starter and solonoid, clean and grease the starter pinion, and clean the contacts in the solonoid, it may be prudent to replace the starter brushes while it is stripped.