A word of advice:
For those who has rubber strap watches. It is recommended that you check your straps annually or every 3 months for straps older than 2 years.
How to check?
1) Visually inspect the whole strap under strong lighting to see if there are any cracks or signs of fatigue apparent. If yes, replace with new strap.
2) Bend the strap in all directions, and give it a twist. Check for any signs of lessened elasticity (ie stiffness) and also signs of cracks and fatigue at the bending point. If yes, replace the strap.
All said, its recommended to replace rubber straps every 2 years or annually which is better.
To make sure straps last longer, wipe down the strap with a soft, damp cloth after every time you wear it. Leave it to air dry before storage.