Several websites offer clocks and countdown timers that can be used for free. Set the parameters and copy the HTML code, usually just an iframe, into an HTML block.
For example, the following code gives the HTML block 'ANALOG CLOCK' shown below. The iframe was obtained from timeanddate.com.
<div style="text-align:center;">
<iframe src="https://freesecure.timeanddate.com/clock/i5etbz0j/n165/szw160/szh160/hoc0070a8/hbw0/hfcebebeb/cf100/hgr0/fiv0/fas34/fac888/fdi72/mqv0/mhc888/mhs3/mhl20/mhw2/mhd84/mmv0/hhc888/hhb10/hhw11/hmc888/hml75/hmb10/hmw8/hsv0" frameborder="0" width="160" height="160">
</iframe>
</div>
By adding a few properties as follows, the position of clock can be fixed relative to the browser window, i.e. the clock will not scroll. Here, it would always stay positioned at the lower right corner.
<div style="width:200px;background-color:#f5f5f5;border:1px solid #cccccc;border-radius:0.3em;text-align:center;padding:20px 0px;position:fixed;right:20px;bottom:15px;">
<iframe src="https://freesecure.timeanddate.com/clock/i5etbz0j/n165/szw160/szh160/hoc0070a8/hbw0/hfcebebeb/cf100/hgr0/fiv0/fas34/fac888/fdi72/mqv0/mhc888/mhs3/mhl20/mhw2/mhd84/mmv0/hhc888/hhb10/hhw11/hmc888/hml75/hmb10/hmw8/hsv0" frameborder="0" width="160" height="160">
</iframe>
</div>