As per Pega 7.2, I do not see we can increase the height of DateTime control. I tried adding height attribute to the cell's property as inline style. However, the change is not getting picked up. Adding padding attribute, does increases the space around DateTime control. I am still investigating and will keep you posted.
I'm unsure if we have any option at skin level to modify this but you can try out the below one. It worked fine for me kindly check.
Add below style in userWorkForm and specify your required height
This change would reflect throughout. In case that is not wanted then probably you can add a non-auto generated section with the above style change and add that non-auto generated section in the required section that contains the dateTime control.