If you post some screenshots of what you're talking about, we'll be better able to make suggestions.
This is an interesting issue with bins. One possibility is to create your own bin function and then use it as a continuous field on color. That way it will recalculate the gradient as new values come in.
1. Create a new calculated field called [Custom Bin] (or whatever you want) with the code:
INT([SinceLastModificationHours] / 24) * 24
2. Drag the field [Custom Bin] from Measures to Dimensions.
3. Drag the field [Custom Bin] to Color
4. Make sure the field on the Color shelf is green (continuous). If it is not, right click it and select "Convert to Continuous".
5. Set the color palette to red.
Thank you for the feedback (on a Friday of a long weekend yet!). It seems to work!!! I'll know for sure over the next week or so, but thank you! Perhaps it's a bug that my way didn't work??!! But, your workaround was really simple and effective! Thanks!!!!
You're welcome! Glad to help!