Depends on your needs and what devices you have.
If you have a basic smartphone, just use the built-in stopwatch and use the lap feature. Take notes on which times account for what on your phone.
If exact times are needed, as in the actual time (e.g. 3:51 PM MST), then just screenshot the actual clock on your phone. Each screenshot of your clock serves its purpose. Both Android and iOS have analog clocks with a seconds hand to help you account for actual times for those projects that require it.
Shopping the Greater Denver Area, Colorado Springs and in-between in Colorado. 33 year old male and willing to travel!