I think an hour should cover it in terms of conversion of starches in essentially all cases. You can do an iodine test if you want. It is cheap and easy, and will give you something to do while you wait.
Some malts that have fewer enzymes in them (i.e. lower diastatic power) may benefit from longer mashes. For example, Great Western Premium 2-row has a diastatic power of 140 Lintner, and will probably convert pretty fast, while Munich only has a distatic power of 40 Lintner. If you use all Munich, plus kilned or roasted malts that have no enzymes, it will take longer for the reduced enzyme concentration to fully convert the mash. A recent article in BYO magazine (https://byo.com/article/brewing-by-ratio/ ) says that the average diastatic power of your gran bill (weighted average of individual malts in the mix) should not be lower than 40, so a mash like the one I just described should be avoided. Adding a bit of high diastatic power 2-row would be helpful.
Temperature also makes a difference, but not in a simple way. Chemical reactions go faster at higher temperatures, so conversion happens faster, but the enzymes also get denatured faster so their lifetime is shorter at high temperatures. If you have plenty of enzymes, then the shorter lifetime is not a problem, but if you are low on diastatic power in the first place you may find that a higher temperature does not give you faster conversion.
The bottom line for me is that patience is a virtue and I shouldn't try to rush the mashing process. I always calculate the diastatic power of my grain bill and try to keep it high enough that an hour mash should be plenty of time.
--GF