Command line – Convert string on time using shell

I have a shell script that will bring the time (h: m: s) of the database and compare it with the current time to perform an action based on the result of the comparison.

I get the current time using this command

current time = $ (date +% H% M% S);

the time I received from the database that is peak_time with this format
H: M: s
So I eliminated the: from that moment using this code.

    peak_time = `$ peak_time & # 39; | thirst s /: // g `

and now I need to convert the last result in time using this command

    peak_time = $ (date -d "$ peak_time" +% H% M% S);

but I get this error

date: invalid date '190000'

so please tell me how can I solve this problem