in very official case, we say 七点二十八分 for example in news etc. in ordinary cases, we say 快(almost)七点半了 or 差几分钟七点半 or 差两分七点半(two to seven) we can also say 七点半 even it is 7:28 some examples: 7:03------七点多了 7:14------快七点十五了 or 快七点一刻了（一刻 means a quarter） for 差不多七点半 u must pay attention: u can just use this when it hasn't arrived 7:30. If it has surpassed 7:30, such as 7:31 7:32 etc, u must say 七点半多 P.S. for all of 了 here, it doesn't mean the pass, so 现在七点多 = 现在七点多了 了 here just highlights the fact that it has passed seven o'clock.

七点半 is used more frequently in daily life. and you do not have to use 差不多, although I can not tell why. We just use 七点半（了）

both of them is ok.your chinese is eally good!

现在差不多七点半

The more common way to say it's almost half past seven is 快七点半了。 If it's a little after 7:30, you can say 七点半多了。 And 七点半左右 or 差不多七点半 is ok for both.