Bash Script – How to Measure Program Execution Time and Store in a Variable

In order to find out how long certain operations within a Bash (v4+) script take, I would like to parse the output from the time command "separately" and (ultimately) capture it within a Bash variable (let VARNAME=...).

Now, I am using time -f '%e' ... (or rather command time -f '%e' ... because of the Bash built-in), but since I already redirect the output of the executed command I'm really lost as to how I would go about to capture the output of the time command. Basically the problem here is to separate the output of time from the output of the executed command(s).

What I want is the functionality of counting the amount of time in seconds (integers) between starting a command and its completion. It doesn't have to be the time command or the respective built-in.

Edit: given the two useful answers below, I wanted to add two clarifications.

1. I do not want to throw away the output of the executed command, but it will not really matter whether it ends up on stdout or stderr.
2. I would prefer a direct approach over an indirect one (i.e. catching output directly as opposed to store it in intermediate files).

The solution using date so far comes closes to what I want.